EV11 event 41478 - user does not have permission on any archive issue

I have the same issue as described here:

http://www.symantec.com/connect/forums/ev11-event-...

I did what is suggested (delete user row from OWS_UserPreferences table) - this solved the issue, for exactly 2 days.

I had to delete it again today - any ideas how to search for the root cause of this issue?

Thanks,

Sarah