It only started doing this once I got to the Northen Highlands in Act I on nightmare. Each time it crashes I am in the middle of spamming my attacks against a bunch of a goatman.
I am playing Demon Hunter (level 37), and using the Bola Shot with Acid Strike rune, and the Elemental Arrow with Screaming Skull Rune at the moment. I have also just got these skills so maybe its the skills that is causing the crash? Seems to hang while the bola shot is hitting the goatman.
If you want any other information let me know.
-- Post edit.
As soon as I got out of the goatman highland area the crash stopped happening.