Suddenly on multiple Systems: “File system auto protect is malfunctioning”

Hello,

I have a customer with 2000+ SEP 12.1 RU1 MP1 (12.1.1101.401) clients.

Last Friday this error appears on +/- 280 systems: 

"File System Auto-Protect is not functioning correctly. Your protection definitions may be damaged or your product installation may be corrupt."

The systems affected run different versions of Windows. Mostly XP, but also different Windows Server versions and Windows 7 boxes.

This problem can be fixed by running a "repair" of the Client.

However: knowing the fix is one thing, but what I realy want to know why this can suddenly happen on multiple systems at the same time.

Thanks for your input.