One of my colleagues is having the following error message, when trying to open connection from Windows 11 client version 4.1.2.2 to Ubuntu 20.04 server.

Title: Authentication failed.

<ip>:<port> - Verifying that server is a known host: base64 error

I asked ChatGPT and it instructed to remove C:\Users\<username>\.ssh\known_hosts file. That file was removed, but it did not help. The next ChatGPT instructed was to remove this key from Windows registry: HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\SshHostKeys 

There was no such key. User removed the X2go installation and installed it again, no help.

This same Ubuntu 20.04 server is used by other users without any problems.

How to proceed from here?

Thanks,

   Kalle