Matt,
You might put a hotkey in that does a lot of status dumping to a text file to see if you can tell what is going on at the time they experience the problem.
>It all works perfectly 999 times out of 1000, it's just the 1000th time it "freezes" and it just happened to be this form on this occasion and it occurred in my development environment while testing the app. For user's it can happen in various places, sometimes more often than others.