Was about half way through clearing just the trash mobs in terror domain (which mind you was quite annoying me) when after having up a bunch of fire/lightning walls with advocates spamming the crap out of me and black knights charging me all around the screen I decided to go get more health potions from town. Clicked on the town portal and belzebub crashed with a Sfx Error dialog box with "unbind_buffer,, OpenAL invalid operation".
That was quite annoying!
First crash on the beta I have experienced and I've been playing it since release though so I can't really complain.
Just throwing it out there with what I was doing at the time so hopefully it means something to someone.