Win10 can't connect to Win8.1 but Win8.1 can connect to Win10

Thanks for the response.

Re the the link you posted, over the past year and a half I have tried every possible combination of network/sharing settings, including password protecting the shares including your link and many others and nothing worked... again, while the win10 computer in question could not access my other computer, that computer could access the one that would never connect.

For that year and a half, the response to failed connection attempts was that the computer didn't exist... check the spelling... etc... which made no sense since the other computer had no problems connecting, so, the issue was with the first box.

When I finally did "Run \<computername>" I got a completely different error message... essentially "not allowed" which finally lead to more information and the registry entry.

My reading of the MS article is that the setting was protecting me from myself... my main question is "when did things change" since connecting to other computers on the lan worked for years, then got erratic, then "no way"  

I have to believe that this problem and the registry entry was generated in a Win10 update... the other Win10 computers were newer than the problem, and the situation with win8.1 computers was the same, they could connect to the problem computer, but the problem computer could not connect to them... the absence of the parameter in the newer win10 computer confirmed that for me.

Thanks again for the input,

Beverly Howard

(1) Kapil Arya is a well-respected MVP & longtime contributor to these MSFT communities & a great humanitarian. Also, that official MSFT article, although it frowns upon it, does ultimately suggest you may set AllowInsecureGuestAuth that way if you feel you must. Too bad still the results were not permanent. But my suspicion is that not only the computers in your little network would have the ability to do harm to each other but maybe any site they go to might be able to do it, but I can't really say.

(2) Well what about that article I posted earlier...?...

https://support.microsoft.com/en-us/windows/file-sharing-over-a-network-in-windows-10-b58704b2-f53a-4b82-7bc1-80f9994725bf

File sharing over a network in Windows 10

The section "How do I troubleshoot sharing files & folders?" seems to be another way to turn off password protection. Maybe it will stick. Regarding those four services it says to set "Automatic", mine are all set "Manual" except for Function Discovery Resource Publication (the infamous FDResPub) which is set "Manual (Trigger Start)".

I'm thinking, maybe go ahead & make all yours Automatic, but do not turn off password protection. Maybe that will be enough. If not, then go ahead & turn off the protection. I hope that will do it & be permanent.

Sorry for the delay in responding... I'm swamped recovering from this year's Texas storms (both inside and outside)

From my going through the clues the AllowInsecureGuestAuth parameter seems to be there in order to prevent enterprise users from going to guest shares because of the potential of infecting a company network and it makes sense in that environment, but not in a private lan where you need access between computers on your own lan.

With that in mind, I looked at the same registry entry on the computer that COULD access the computer that could not access other shares and found that the AllowInsecureGuestAuth parameter was not in that computer's registry entry.  SO, I went back to the other computer, removed the parameter, rebooted, and still was able to access the computer that had not been reachable when the parameter was present and set to "0"

That would tend to indicate that an update or other action had added that parameter and created the problem over a year ago.

fwiw, here are some url's that helped me get to this point;

https://www.kapilarya.com/fix-you-cant-access-this-shared-folder-because-your-organizations-security-policies-block-unauthenticated-guest-access

This one contains a screenshot of the helpful "group policy" dialog that came up when I used the "RUN \<computername>" https://docs.microsoft.com/en-us/answers/questions/59309/you-cant-access-this-shared-folder-because-your-or.html https://www.youtube.com/watch?v=vyatMj1Z2NQ https://docs.microsoft.com/en-US/troubleshoot/windows-server/networking/guest-access-in-smb2-is-disabled-by-default

I sincerely hope this issue is resolved.

Thoughts and comments solicited,

Beverly Howard

That setting is frowned upon in here...

https://docs.microsoft.com/en-us/windows-hardware/customize/desktop/unattend/microsoft-windows-workstationservice-allowinsecureguestauth

AllowInsecureGuestAuth

But I can't say I fully understand what that article is talking about.

SUCCESS! I finally found the answer to this problem!

I'll post additional information and links when I have time... probably in the next day or so.

The problem is that a "group policy" was set to default to NOT ALLOW CONNECTIONS TO "GUEST" shares. Not sure why, but it looks like this is inconsistent on different installs... perhaps something related to the OEM machine that didn't matter earlier, but got "turned on" probably with updates when this happened over a year ago.

The network connection restriction can be dealt with in a registry entry.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters

The parameter AllowInsecureGuestAuth set this to 1 If the parameter does not exist, add it (watch case) and set it to 1

The file explorer error messages were of zero help, then, today, on a hunch, I entered the name of the computer (\<computername>)using RUN and got a different dialog.

Searching for the text in that dialog found a discussion and a youtube video that showed the above registry entry.

Hope this helps others... it's a shame that other discussions on this problem have been locked and cannot be used to notify those who participated in them.

Beverly Howard