Does anybody have any thoughts or insight into why an exception might be thrown at runtime, either stand-alone or with the Visual Studio debugger, but when you step through the code line-by-line with the debugger, everything works the way it's supposed to?

No idea without the code, though I would suggest that it may be a timing issue (maybe to do with another thread or some asynchronous call).

I agree with TwistMyArm...I've only ever seen that type of problem when there is a race condition or timing issue.

That's what it sounds like, huh? I'm locking all the shared objects when I should be ... except, apparently, in one place that I don't know about. But it definitely sounds like threading issues, right?

The code is a few thousand lines, so posting it here would just bore everybody, but thanks for the sentiment!

There is one other thing that I can think of: when running the program (not debugging it), is it the same build as the one you are stepping through? That is to say, your debug one is obviously 'Debug', but when you're testing it without stepping through it are you still using the 'Debug' build (as opposed to the 'Release' one)?

You probably are, but I just wanted to put this out there: there's a number of times where I've had problems with the 'Release' build but not the 'Debug' one... some things like bad memory access and the like that 'Debug' apparently is OK with.

Thanks for the tips; I've been doing some reading since you mentioned this, and it's 2 am, so my IQ has dropped by 30 points, but it looks like there are some aggressive optimizations in release mode I might need to turn off. Maybe I'm on the wrong track, but I need to look into this stuff when I'm more alert.

Thanks!