Just to bring this up again, this is happening to me too, a lot more frequently. (Still using r168). It always happens while previewing and really weird things happen (Windows error sound plays multiple times, event sheet visually glitches). The computer I'm using is a gaming rig and extremely powerful.
I haven't counted objects, but my guess is it's around 500.
Let me know if you'd like me to send the capx file.
[EDIT] - here's a thought... what if autosave has something to do with it? Maybe C2 crashes if the autosave interval comes up right when previewing? Since it seems to happen without any user input causing it (i.e. in the background while previewing) this would make sense. I'm afraid to turn autosave off to test it however