Don is right probably file ownership problems.

This can alos cause a problem.

You assign a systems person to manage the app. Over time from that person having logged in, did things that change the owner to that person. That person leaves and is removed from the system. Now you have fox files whose owner signiture no longer exist in the system.

Rule: always keep ownership abstract to something that never changes.

I was flown to Chicago from DFW to learn this on an app that all of a sudden quit working. By the time I got back it was all over the message boards. Not my situation but others discovering it at the same time I was.