Sorry about that.
Did you talk to Elder Ankhumar (room 1) after the summoning instructor said you could proceed?
If he doesn't unlock the door, you can use the technique described in the topic
armory trick in act 1 to get a summoning doll through the door, and then have it enter the BF, to get your main characters past the door when you return to the main game.
alternately:
Teleporting anywhere (via hex editor)
