Try starting a new game, then save and use iZakaroN's SaveEditor to bump up the character's constitution, then run to Ars Magicana and see if the same problem occurs.

Have you met Tingalf, the black market dealer, yet? He approaches in a cut scene around that area (he approached me just east of the Ars teleporter pad).
Maybe one of the graphics or sound effects used there became corrupt? Did you try the file verification method mentioned in the troubleshooting/manual install post?