"WindowsUpdate_80240020" "WindowsUpdate_dt000"

According to https://support.microsoft.com/en-us/kb/910341 (cited further down by someone else, which is how I became aware of it), it means that

"the Automatic Updates service cannot impersonate the logged-on user to finish downloading and installing the update"

I, myself, am happily /not/ installing Windows 10, although Windows Update is failing to "Upgrade to Windows 10 Home" on a daily basis because of this problem. Hooray for the problem! May it last forever!

Note that, while I did reserve a copy initially, when I finally read the compatibility report and found that MY VIDEO CARD WAS NOT COMPATIBLE even thought Microsoft was blandly claiming that Windows 10 would run on my computer I de-reserved it. Microsoft, however, appears to be unable to take "no" for an answer.

But what I find most interesting is that the "Upgrade to Windows 10 Home" update is labeled "Important". Important to Microsoft, perhaps, as adding one more bot to the world's largest bot-farm; but unimportant to me.

Still, if you actually /want/ Windows 10, the advice concerning the SoftwareDistribution directory should work. That sort of thing worked in XP, why not a more modern Windows?

Read this answer: Source

Here is how you do it:

1. First you have to go to Windows Update: Control Panel> System and Security> Windows Update. Then activate automatic updates.
2. Go to the folder C:\Windows\SoftwareDistribution\Downloadand erase everything inside.
3. Open an instance of the command line (CMD) with administrator permissions. In Windows 8 you can do this by right-clicking on the Windows button in the lower left corner.
4. Type the following command but do not run it yet: wuauclt.exe/UpdateNow
5. Return to Windows Update. Click on Find Updates, this will make it start searching for all available updates.
6. While it’s searching for the updates, go to the command line and press Enter to execute the earlier command (wuauclt.exe/UpdateNow).
7. Windows 10 should then begin downloading, with the Windows Update screen displaying a clearly visible blue icon.
8. Enjoy!

I'm beginning to think something else is going on. My new laptop converted to Win 10 without a problem. All of my office computers are unable to update. About their computers, Dell in effect says that they're too old to upgrade since they haven't been tested as Win 10 able.

Dell, and HP seem to want you to buy a new computer. They aren't interested in computers over 3 years old, even if they have the power and  memory to upgrade.

Here's exactly what Dell says at http://www.dell.com/support/article/us/en/19/SLN297954

Inspiron Desktop

The table below lists Dell Inspiron Desktop computers that have been tested for upgrade to Windows 10. If your computer model is not listed, the hardware has not been tested and drivers have not been updated for that model, and Dell does not recommended an upgrade to Windows 10.

Get that? Hardware not tested, no updated drivers.

@Alex. 

Great. Respect!

Thank you very much for this share... I worked for me...