Uuups! Unexpected error... | Cannot load the web interface

[Skyfay]

I had version 215 in which everything worked. Now I've upgraded to the latest one and I keep getting this error.

I also reinstalled it directly to this version once, but I got the same error.

Can anybody help me further?

[martinpitt]

You didn't give much information (OS, installed package versions), but my first guess is that you upgraded some basic cockpit packages from Ubuntu backports, but did not upgrade cockpit-machines? Please try

sudo apt install -t focal-backports cockpit-machines

[Skyfay]

Many thanks for the answer. In fact, I've issued this command before during my search.
But now it worked, everything is running again. Thanks very much.