@maksaab what if you restart your computer and launch Manager again. Same issue?
@maksaab, please do not divert topics with unrelated questions. Yours had nothing to do with activation keys. It is only by chance the developer saw it. Your question has been moved to a new topic.
yes
@maksaab, the software version in your screen shot is hundreds of versions out of date. Have you updated since?
no
Then update.
Updated a very old setup by removing and reinstalling(v20.5.2). Now I get this error! 
What platform and Operating System are you using?
Did you download from the official site www.manager.io?
Windows 8, Yes. Downloaded from Manager.io
Did you follow the Guide for Windows installation and update?
Yes
@yasiph looks like you will need to install .NET Framework 4.6.1
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