I accepted the quest "The Divination" from Thadius Grimshade in the blasted lands, which he gave to me after handing in a Zul'Farak Quest. The quest simply asks me to wait a moment and then talk to him again.
Now when I talk to him again, I see the Quest-Completion dialog, but when I click "Complete Quest", nothing happens. I have to click "Cancel" and can't finish it.
Could you please have a look?
LVL 45 Human Warlock Rodderick
Quest description in detail: http://db.vanillagaming.org/?quest=2992
EDIT: Solution
After receiving no reply, I decided to abandon the quest, taking the risk of losing the quest chain. Fortunately, I could take the quest again and let Grimshade do his ritual. This time, it worked and I could hand in the quest as well as accept the following quest in the chain.