Now I am confused.
I have noticed that this bug also affects our game:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=613221(One main character, Lohse in our case, does have no audio for her lines in the party dialogue events)
I recreated the dialogue event that led to a crash yesterday, but now it worked without crashing the game (only skipped audio for Lohse).
But could anyone tell me if the two main characters should be able to talk to each other at all times (which I assumed), or if they can only talk to each other during certain "yellow exclamation mark" events? If so, then my alleged bug is not a bug, but a feature, and we are affected by another bug (skipped audio lines for Lohse).