I'm sure the admins are aware of this, but incase this helps any, this is what I've tested and surmised:
Campaign/Single Player Mode: After 1-8 minutes I crash to desktop, audio repeats and I have to quit CXgames 8.1.3.
Scavenger/Survival Modes: I can play full rounds, change to next round and continue.
Possible Problem: It seems my game crashes when it has to load new map/zombie information into memory. I can play Scavenger and Survival modes because the maps are locked to a specific area (no reloading of map) and the maps are smaller.
Hope this helps.