Game Crashing in act 6 areas

i tried 2 different characters, my 51 Ranger and my 70 witch.
both are crashing in act 6 areas, other than Lioneye's watch.

i first noticed the crash when i was using the steam version, as soon as i walk in an area in act 6, 3-10 seconds later the game crashes. i thought i should try just walking, not fighting not doing any spells. it kept crashing. i tried going back to act 5 or going forward (with another character) to act 8, no crash occurs, i am able to fight and walk as much as i want. however, as soon as i go into an act 6 area, the game crashes.