outlook 2007 cannot display email while it is open and after closing cannot reopen

Question

outlook 2007 cannot display email while it is open and after closing cannot reopen

David 1 10

After I establish a remote desktop connection my outlook 2007 will not display a email in the reading pane, if i close outlook and try to reopen it will not open and get this error: User's image

if I try to go in safemode thru win R then i same error but 1st time trying it was a extend.dat error but after deleting that file it is now same as above. The only remedy i have success with is reboot. but i use remote desktop everyday and it is a pain in the ass to have to keep doing this

Hornblower409 14,815 Reputation points

2026-06-18T00:26:59.91+00:00
@David 1

1 -- Do I understand correctly?

You remote into a PC.

You start Outlook.

All is good.

You end the Remote Session. (Outlook is still running)

You re-connect the Remote Session and you get the error when you try to open an email

2 -- When you Close Outlook have you confirmed that Outlook is really dead by checking Task Manager?
David 1 10 Reputation points

2026-06-18T06:32:54.6866667+00:00

No i open outlook and all is good , i leave it open all day. I open my browsers and still all is good, then i open a Remote Desktop connection and sometime shortly after that when i go to click on a email it says cannot show in the reading pane, i shut outlook and try to reopen but it will not open. If you go to task manager it doesn’t show any open outlook. Cannot go into safemode for outlook either. Only solution i know of is to reboot, don’t see what Remote Desktop has to do with it
Hornblower409 14,815 Reputation points

2026-06-18T13:59:43.2866667+00:00

@David 1 said

open outlook and ... leave it open all day
i open a Remote Desktop connection and ... [Outlook] cannot show in the reading pane

Got it. It's Outlook on your desktop that goes wonky, not Outlook on a remote.

Cannot go into safemode for outlook either

I can't test with Outlook 2007, but what I read says the /safe switch is supported.

[External Non-Microsoft Site] https://robert365.com/article/commandlineswitches

You talked about problems with Safe Mode in your original post but I don't understand. Can you try to explain the sequence again? Screen shots of any errors would also help.

don’t see what Remote Desktop has to do with it

Same here. I can't think of anything that RD could do that would make Outlook panic.
Hornblower409 14,815 Reputation points

2026-06-18T14:13:14.4633333+00:00

David

It's as if RD is opening a handle to the Outlook data directory and won't let go. Is your RD connection setup to share any local resources except the defaults?
David 1 10 Reputation points

2026-06-18T16:25:34.8566667+00:00

YES "Got it. It's Outlook on your desktop that goes wonky, not Outlook on a remote." The first time i tried to go into OUTLOOK safemode by holding the ctrl key while clicking on the outlook icon i got an error about an extension failed to initialize. cannot open file extend.dat. the file may not exist, you may not have permission to open it, or it may be open in another program. Upon google that error it told me to either rename extend.dat or delete it. After doing that I no longer got that error instead i received

but still could not get into safe mode unless restart computer first

i dont have any local resources for the RD being specified, just clipboard and smart cards
Hornblower409 14,815 Reputation points

2026-06-18T20:28:19.9366667+00:00

David said

still could not get into safe mode unless restart computer first

That's expected. If a copy of Outlook is still running, you can't start a new copy thru any means.

If you go to task manager it doesn’t show any open outlook

Need to nail this part down first.

It's not unusual for Outlook to not be visible but still running in the background. It may not be in at the top under Apps in Task Manager. Look down the list. If you see it, right click and [End Task]. Does it go away? Can you then start up a new copy normally?
David 1 10 Reputation points

2026-06-19T05:30:23.9166667+00:00

No not showing that outlook is running anywhere in task manager
Hornblower409 14,815 Reputation points

2026-06-19T12:22:11.9733333+00:00

6 -- @David 1 said

"cannot open file extend.dat" ... Upon google that error it told me to either rename extend.dat or delete it

I think you were only suppose to unhide it.
https://learn.microsoft.com/en-us/answers/questions/4764830/opening-outlook-2007-error-message-referring-to-ex

Regardless. I'm still not clear on the sequence. Is this right?

1 -- From a reboot

2 -- You open Outlook - All is good

3 -- You can exit Outlook and start it again - All is good

4 -- You open a RD Session.

5 -- What happens to Outlook at this point? Is it still open?

6 -- You close the RD Session? Or just switch to the Outlook window?

7 -- You can still see your messages in Outlook but if you click on one to open it, you get the "Cannot open your default email folders".
David 1 10 Reputation points

2026-06-19T18:31:12.27+00:00

I can open and close outlook until this error occurs but it usually remains open all day as well until i experience the error I usually have RD open all day as well, I can see the messages but when i click on one to read in reading pane and it doesnt load it there then i know that once i close outlook wont be able to open again without restart computer
Hornblower409 14,815 Reputation points

2026-06-19T23:53:57.8033333+00:00
@David 1
I really don't know what is causing your problem, so all I can suggest are The Usual Suspects

Office Repair

Control Panel -> Programs and Features

Find Microsoft Office 2007 in the programs list, right click it, then select Change.

Once open, select Repair then Continue.

Run Outlook in Safe Mode (But you said you can't make that work)

Open the Windows Run dialog: Windows Logo Key + r

Open: "C:\Program Files (x86)\Microsoft Office\Office12\outlook.exe” /safe

[OK]

Create a new Outlook Profile

Control Panel -> Mail

Show Profiles -> Add

{Complete the new Profile setup}

Prompt for a Profile to be used
David 1 10 Reputation points

2026-06-23T14:29:59.5466667+00:00

I tried running office repair but it wont complete successfully.
David 1 10 Reputation points

2026-06-23T14:32:56.5+00:00

I can run in safe mode after restarting but not once the problem happens
Hornblower409 14,815 Reputation points

2026-06-23T19:21:52.03+00:00

@David 1 said

I tried running office repair but it wont complete successfully

Not good. Not much point in trying anything else if the installed code is that broken.

I am reticent to suggest anything at this point for fear of just making things worse.

But - If you can make a full backup of your entire system first, you have the original install media, and your Product Code Key, then all that's left is to completely uninstall and re-install from scratch. If it fails, you'll have to do a full restore from your backup. Proceed at your own risk.

The only other option I can think of is to buy a new Office version. e.g. Licenses for standalone Office 2019, 2021 are pretty cheap. Full uninstall 2007 and go from there.
Hornblower409 14,815 Reputation points

2026-06-23T19:31:54.8933333+00:00

David

! Before your do anything - Do a full Export to a PST of all of your current Outlook data.

"Classic Outlook" tab at
https://support.microsoft.com/en-us/outlook/export-emails-contacts-and-calendar-items-to-outlook-using-a-pst-file

Import
https://support.microsoft.com/en-us/outlook/import-email-contacts-and-calendar-from-an-outlook-pst-file
David 1 10 Reputation points

2026-06-25T14:22:06.8166667+00:00

I ran dism a day or 2 ago and it said it made repairs, so far no problem now. Not sure what it fixed but I will see how it goes for a few more days and let you know
David 1 10 Reputation points

2026-06-28T05:10:13.2566667+00:00

No problem since i ran dism
Hornblower409 14,815 Reputation points

2026-06-28T13:35:46.9833333+00:00

@David 1 said

No problem since i ran dism

Thanks for the progress report. I'll add DISM to my list of "What to do when nothing else works".

1 answer

Your answer

Hornblower409 14,815 Reputation points

2026-06-18T00:26:59.91+00:00

@David 1

1 -- Do I understand correctly?

You remote into a PC.

You start Outlook.

All is good.

You end the Remote Session. (Outlook is still running)

You re-connect the Remote Session and you get the error when you try to open an email

2 -- When you Close Outlook have you confirmed that Outlook is really dead by checking Task Manager?
David 1 10 Reputation points

2026-06-18T06:32:54.6866667+00:00

No i open outlook and all is good , i leave it open all day. I open my browsers and still all is good, then i open a Remote Desktop connection and sometime shortly after that when i go to click on a email it says cannot show in the reading pane, i shut outlook and try to reopen but it will not open. If you go to task manager it doesn’t show any open outlook. Cannot go into safemode for outlook either. Only solution i know of is to reboot, don’t see what Remote Desktop has to do with it
Hornblower409 14,815 Reputation points

2026-06-18T13:59:43.2866667+00:00

@David 1 said

open outlook and ... leave it open all day
i open a Remote Desktop connection and ... [Outlook] cannot show in the reading pane

Got it. It's Outlook on your desktop that goes wonky, not Outlook on a remote.

Cannot go into safemode for outlook either

I can't test with Outlook 2007, but what I read says the /safe switch is supported.

[External Non-Microsoft Site] https://robert365.com/article/commandlineswitches

You talked about problems with Safe Mode in your original post but I don't understand. Can you try to explain the sequence again? Screen shots of any errors would also help.

don’t see what Remote Desktop has to do with it

Same here. I can't think of anything that RD could do that would make Outlook panic.
Hornblower409 14,815 Reputation points

2026-06-18T14:13:14.4633333+00:00

David

It's as if RD is opening a handle to the Outlook data directory and won't let go. Is your RD connection setup to share any local resources except the defaults?
David 1 10 Reputation points

2026-06-18T16:25:34.8566667+00:00

YES "Got it. It's Outlook on your desktop that goes wonky, not Outlook on a remote." The first time i tried to go into OUTLOOK safemode by holding the ctrl key while clicking on the outlook icon i got an error about an extension failed to initialize. cannot open file extend.dat. the file may not exist, you may not have permission to open it, or it may be open in another program. Upon google that error it told me to either rename extend.dat or delete it. After doing that I no longer got that error instead i received

but still could not get into safe mode unless restart computer first

i dont have any local resources for the RD being specified, just clipboard and smart cards
Hornblower409 14,815 Reputation points

2026-06-18T20:28:19.9366667+00:00

David said

still could not get into safe mode unless restart computer first

That's expected. If a copy of Outlook is still running, you can't start a new copy thru any means.

If you go to task manager it doesn’t show any open outlook

Need to nail this part down first.

It's not unusual for Outlook to not be visible but still running in the background. It may not be in at the top under Apps in Task Manager. Look down the list. If you see it, right click and [End Task]. Does it go away? Can you then start up a new copy normally?
David 1 10 Reputation points

2026-06-19T05:30:23.9166667+00:00

No not showing that outlook is running anywhere in task manager
Hornblower409 14,815 Reputation points

2026-06-19T12:22:11.9733333+00:00

6 -- @David 1 said

"cannot open file extend.dat" ... Upon google that error it told me to either rename extend.dat or delete it

I think you were only suppose to unhide it.
https://learn.microsoft.com/en-us/answers/questions/4764830/opening-outlook-2007-error-message-referring-to-ex

Regardless. I'm still not clear on the sequence. Is this right?

1 -- From a reboot

2 -- You open Outlook - All is good

3 -- You can exit Outlook and start it again - All is good

4 -- You open a RD Session.

5 -- What happens to Outlook at this point? Is it still open?

6 -- You close the RD Session? Or just switch to the Outlook window?

7 -- You can still see your messages in Outlook but if you click on one to open it, you get the "Cannot open your default email folders".
David 1 10 Reputation points

2026-06-19T18:31:12.27+00:00

I can open and close outlook until this error occurs but it usually remains open all day as well until i experience the error I usually have RD open all day as well, I can see the messages but when i click on one to read in reading pane and it doesnt load it there then i know that once i close outlook wont be able to open again without restart computer
Hornblower409 14,815 Reputation points

2026-06-19T23:53:57.8033333+00:00

@David 1
I really don't know what is causing your problem, so all I can suggest are The Usual Suspects

Office Repair

Control Panel -> Programs and Features

Find Microsoft Office 2007 in the programs list, right click it, then select Change.

Once open, select Repair then Continue.

Run Outlook in Safe Mode (But you said you can't make that work)

Open the Windows Run dialog: Windows Logo Key + r

Open: "C:\Program Files (x86)\Microsoft Office\Office12\outlook.exe” /safe

[OK]

Create a new Outlook Profile

Control Panel -> Mail

Show Profiles -> Add

{Complete the new Profile setup}

Prompt for a Profile to be used
David 1 10 Reputation points

2026-06-23T14:29:59.5466667+00:00

I tried running office repair but it wont complete successfully.
David 1 10 Reputation points

2026-06-23T14:32:56.5+00:00

I can run in safe mode after restarting but not once the problem happens
Hornblower409 14,815 Reputation points

2026-06-23T19:21:52.03+00:00

@David 1 said

I tried running office repair but it wont complete successfully

Not good. Not much point in trying anything else if the installed code is that broken.

I am reticent to suggest anything at this point for fear of just making things worse.

But - If you can make a full backup of your entire system first, you have the original install media, and your Product Code Key, then all that's left is to completely uninstall and re-install from scratch. If it fails, you'll have to do a full restore from your backup. Proceed at your own risk.

The only other option I can think of is to buy a new Office version. e.g. Licenses for standalone Office 2019, 2021 are pretty cheap. Full uninstall 2007 and go from there.
Hornblower409 14,815 Reputation points

2026-06-23T19:31:54.8933333+00:00

David

! Before your do anything - Do a full Export to a PST of all of your current Outlook data.

"Classic Outlook" tab at
https://support.microsoft.com/en-us/outlook/export-emails-contacts-and-calendar-items-to-outlook-using-a-pst-file

Import
https://support.microsoft.com/en-us/outlook/import-email-contacts-and-calendar-from-an-outlook-pst-file
David 1 10 Reputation points

2026-06-25T14:22:06.8166667+00:00

I ran dism a day or 2 ago and it said it made repairs, so far no problem now. Not sure what it fixed but I will see how it goes for a few more days and let you know
David 1 10 Reputation points

2026-06-28T05:10:13.2566667+00:00

No problem since i ran dism
Hornblower409 14,815 Reputation points

2026-06-28T13:35:46.9833333+00:00

@David 1 said

No problem since i ran dism

Thanks for the progress report. I'll add DISM to my list of "What to do when nothing else works".

Answer 1

The issue occurs because Outlook.exe continues running in the background and keeps the .pst file open, so Outlook cannot reopen and shows the “file is in use and cannot be accessed” error.

Use these steps when the problem occurs instead of rebooting:

End the hidden Outlook process
1. Press Ctrl+Shift+Esc to open Task Manager.
2. Go to the Processes (or Details) tab.
3. Look for OUTLOOK.EXE.
4. Select it and choose End Task.
5. Start Outlook again normally.
Start Outlook in Safe Mode and disable add-ins
1. Press Win+R.
2. Type outlook.exe /safe and select OK.
3. In Outlook, go to File > Options > Add-ins.
4. At the bottom, next to Manage, select COM Add-ins and choose Go.
5. Clear the check boxes for all add-ins to disable them (do not select Remove).
6. Choose OK, then File > Exit to close Outlook.
7. Start Outlook normally. If it works, re-enable add-ins one at a time and restart Outlook each time until the add-in that causes the problem is found. Leave that add-in disabled.
Reset the Navigation Pane (if Outlook still will not open)
1. Close Outlook.
2. Press Win+R.
3. Type Outlook.exe /resetnavpane and select OK.
4. Start Outlook again.

If Outlook continues to hang or not respond, run the Classic Outlook Advanced Diagnostics troubleshooter as described in the Outlook “not responding” article to check for profile, data file, or add-in issues.

References: