To fix the update install failure. WTL ( three possible solutions)

[moyens]

To fix the update install failure. (three possible solutions)

You go to:
C:\ProgramData\Watchtower\WTLibrary

and delete these two files:

ca-bundle.zip
cert.pem

That's all.

PS: If you don't see "ProgramData" in your C you may need to unhide hidden folders.
You can do that in:  Control Panel / Appearance and Personalization / Folder Options / Sow Hidden Folders.
Then in the View tab of the window that pops up select "Show hidden files, folders, or drives."
Then hit Apply and then OK

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Another  solution:
The solution that worked was to manually download the extended all-time update from the following link and then call up the "Import Update Package“ menu item on the software.

https://www.jw.org/en/online-help/watchtower-library/update-watchtower-library/#p15

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And another:

I had the same issue that has been going around. On one computer I have windows 10 2004 update.  On another one I have windows 10 1909 with all updates. I also have a surface pro with windows. 
 
I also deleted WTLib and reloaded the ISO. It did not work.
 
At one point none of them would update regardless of OS version. I signed in as Administrator
and all of them loaded the update. 
 
That's all.