I just noticed today that my MOM/ForeFront server wasn't working anymore, so
I've worked backwards and I notice now that SQL cannot open the OnePoint
database via the SQL Management studio.
I've checked the logs and it says:

I have a rule that each day calculates a performance counter to
measure the size of a folder (this uses a custom script I wrote
because the built-in method did not allow to calculate size of very
very very large folders).