When the underlying authentication service breaks (e.g. network connection loss for ldap login), there is no indication to the user other than "Unlocking failed".

Plasma 4's lock screen would at least show "Authentication failed because the underlying service isn't working correctly" (or something like this) so you at least knew you weren't mistyping your password 10 times in a row.

In ConvPutAuthError it probably should emit error with a message instead of just emitting failed