I had another type of error on 12.04, the 'users' command used for checking of logged users doesn't return all active users in the Unity. Time of such user is not counted and he's not logged out after expiration of the allowed time.
The problem is in the /usr/share/python-support/timekpr/timekpr.py file, method getusers(), line 124 .
I've used workaround using 'ps -e -o ruser' command instead of 'users'.
Patch is attached.