Ardanus, which one did you kill? The one in a cave? that's the wrong one. The one in Verdistis? that's the correct one - but there are other ways to bust this quest:
Have you had the Drudanae quest by George? Or did you refuse to give him the drug plant? Then it will remain unsolved.
Did you talk to Mardaneus after killing? Only he can give you the XP for the quest - if... you haven't refused the Drudanae quest.
Kiya
