I just ran into the exact same problem in denerim. except with me the crash would either happen upon entering the market district from either a store or coming back from the pearl or abandoned house etc. or if I loaded a save inside the market district. I can however go into the market district from camp and other places on the world map. and I can load a save provided I load another first. But I want to point out that I had none of these problems until now and im 50 hours into the game. I experimented with several different saves and I think I have isolated the bug to when I completed the "paragon of her kind" quest. This is the first main quest I have completed and I'm pretty confident that basically taking the main story to the point where lothering is destroyed and the blight has spread is what set off the bug. There are a lot of changes that happen all over the game (especially denerim) after lothering is destroyed and im putting my money on that being where the bug is. Also I want to point out that while I am using a TON of mods, improved atmospheres actually was not one of them. also when I was experimenting with my before and after "lothering destroyed" saves, I disabled NONE of those mods and the CTD was not happening. ok it did crash SOMETIMES but it wasn't so bad that I couldn't load a save in denerim or walk in and out of a store. I hope this points somebody in the right direction of coming up with a real fix to this highly annoying and almost game ruining bug.
