[Gajim-devel] Has errors: remote-server-not-found

[info]

After a hard drive crash I had to reinstall the XMPP server and restore 
its DB from backup.
Everything in the server seems to have been restored back to its state 
before the crash, at least the users are there and each of them can 
still connect their Gajim after accepting the new SSL cert.
But their rosters have an issue: each contact is offline with a 
red-white X icon and their info says

Has errors: remote-server-not-found

How can I purge this state from the roster contacts and let the users 
communicate again?

Thank you
Alex