I assume you tried reloading and re-entering the treasure room? The door should be unlocked, but I'm not positive about this. Maybe there is a lever to unlock it somewhere or a key? It's been a while since I played that part.
If you're really stuck, maybe try the HEX editor.
http://lariancom.siteprotect.net/ub...&sb=5&o=&fpart=1 -- it'll simulate "teleport."
