on my Laptop=Dell latitude E6510, RAM=8Gb, GPU=GT218 NVS 3100M, CPU=i7 Q 720 @ 1.60GHz running opensuse leap 42.2, plasma 5.9.1, KDE frameworks 5.30.0, KDE applications 16.12.1, Kernel 4.4.36-8-default, nvidia drivers
I logged in with user "pla" then switched to user "nipoti" and everything gone well, then switch back to user "pla" and everything gone well, then switch back to user "nipoti" and this error appeared:

the screen locker is broken and unlocking is not possible anymore.
in order to unlock switch to a terminal (e.g. ctrl+alt+f2).
login and execute the command:
loginctl unlock-session
afterwards switch back to the running session (ctrl+alt+F8)

I tried but it doesn't worked.
how to avoid this error??
manythanks, ciao, :-) pier :-)