I have an application written in VB.Net. It uses a dll to talk to an
external device. Initially, it was all written in one thread, and it
worked fine. I need to take readings from the external device at
regular intervals, so now when the application loads, I create a
thread that just loops and reads, sleeps.

However, once I make the application multithreaded, the non-reading
thread exits all the time with no apparent reason. It occaisionally
throws a System.ExecutionEngineException which comes up and says that
one of my forms cl***es is null, but which cl*** varies depending on
the run. Other times, it just exits without any error, unexpectedly.
The cl***es certainly aren't actually null, as I can sometimes pull up
5 or 6 instances of the form and then the 7th with throw the
exception.

Because the application just quites, I'm having a really hard time
determining where the error is, or how I can troubleshoot it best.
From what I've been able to find out about the
System.ExecutionEngineException, it sounds like it could be a problem
with the dll. But if that is the case, why does it only show up when
I multithread the application?

Can anyone provide some advice on how best to pursue this?

Thanks in advance,

-SC