Try running the configuration program and switching to software mode, and maybe reduce the resolution, until you get past that point.
If you lead the succubus back to where Zandalor is, does that make any difference?
Try deleting all of the files in the '..\Divine Divinity\Run\Dynamic' folder. If you reset the configuration after one of the times it crashed, I think this should already have been done.
This folder is used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied from that folder when you save a game. The files will be re-created as required the next time you start Divinity. If there was a corrupt file in that folder, deleting the files should fix the problem.
While searching for the key to Mardaneus' house, did you check Lanilor's house? A black ring member should have approached from there in a cutscene when you got close.
