I've just completed this myself and ...


It did take a while for everyone to gather at the table, so you may just need to wait a minute. The first time I talked to Barcus, I just got the normal dialogue too, but then I left it a while and tried again, then got the dialogue to say I'd rescued Wulbren, after which I could go and talk to them over at the table and complete the quest.

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"