The source environment was Moodl 1.8.2+
I created a very simple and quite empty course.
I created two categories ("produttore" and "cav") and I had one user per category enrolled into my quite empty course.

I made a backup of this course requiring user.

I went to a different server.
I made a CVS update (half an hour ago, saturday September 29 8:00 a.m. italian time).
I called the page "notification"
and I restored the course coming from the different server backup.

Attached is the error I got.