Nothing in particular - I just play on various servers I favorited and after a short period of time (anywhere from 10-30 minutes) the game crashes to desktop. The last crash I had occurred after corralling a horde of around 10-15 zombies outside in Elektro (my character was kaput after that). Other crashes occurred while I was in buildings looking for supplies or other normal scenarios. Servers were low-pop at the times of the crashes and always under 50-ping.