I had the same problem... the instructor would keep telling me I missed an item, also did the summoning book.
I went back to the library, read all books again AND I put the one that describes mycology in my inventory... when I entered the summoning room with this extra book it worked! <img src="/ubbthreads/images/graemlins/wave.gif" alt="" />
Actually, I already got the XP the moment I walked in the room.
The book had to be in the inventory to trigger the quest.
Apparently the Larian people think we take all books with us (maybe some of you do)...
