If you are running ubuntu 20.04 on Windows Server using WSL 1 you might get this error if you remove the Ubuntu filesystem folder, but WSL is still registered to a live distribution.
To fix, get a list of the registered distributions:
wslconfig /l /all
Windows Subsystem for Linux Distributions: Ubuntu-20.04 (Default)
Unregister this distrubution
wslconfig /u Ubuntu-20.04
Unregistering…
Then re register the distribution
ubuntu2004.exe
Installing, this may take a few minutes…
Please create a default UNIX user account. The username does not need to match your Windows username.
For more information visit: https://aka.ms/wslusers
Enter new UNIX username:
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