I have an application which has worked fine for the last ~3 years. Right now though, it's started throwing an exception;

"System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

This occurs when running a sub in an external DLL (which is one my own DLL's). This has only started within the last month or so and happens on the same computer it was developed on and happens if I open the source and run it in the IDE. I cant see anything wrong with the code, if I skip over the sub it crashes on, it then crashes on the next sub.

Oddly, it also seems to only crash the first time it runs a sub within the DLL. So if I run the same sub 10 times, it only crashes on the first execution of it, the next nine times are fine.

I suspect it may be caused by KB939373 (security update for XP) or KB936357 (update for XP). It might also be some kind of initialization problem where the DLL cannot be read or something as the program starts up.

Anyone else seen this?