My game is also causing a crash after installing dawnguard. Uninstalled all my mods ect. When I get serena on the first quest as I get close to the door inside to leave boom crash! Now that im out it seems constant about 30 mintues of playing and I get a crash. Even started a new game currently level 18 stealth nightingale. It sucks but I am trying my hardest to figure this out. I just can't play skyrim without these mods though, Deadly Dragons, Frostfall Hyperthermia, Filling food and restfull sleep, camping kit of the northern ranger. Sabre Backpacks, I love skyrim to be immersive as real as possible when playing. But I will say just playing dawnguard for that little bit of time was AWSOME! HAHAHAH!