Took awhile to figure out what was happening. ugh.
It turned out when I would edit a variable, it would leave out the variable name, (without my noticing) causing a crash to desktop at the next preview or save. It only happens when a constant global variable is present in the project.
<img src="https://dl.dropbox.com/u/85412219/forumposts/variablecrash.png" border="0">
https://dl.dropbox.com/u/85412219/forumposts/variablecrash.capx
edit event 2 and see the variable name is blank like the image. If you catch it when it happens, or return to fix it when you see the name in the event has changed to {0} then you will avoid the crash.
I had something similar in the past as well, but I could only track down that it was a problem with a static variable, I just avoided static variables ever since. This is probably what happened.
R108.2 64 bit win7
[edit: made the capx link clickable]