I finished "A Dark Threat Looms" (Loch Modan) where I put the disarming Mixture into the barrel, then it showed me the next quest, I tried to accept and it said "You dont meet the requirements for that quest" and I couldnt accept it anymore, if I talk to the barrel now nothing happens. After all I couldnt even "talk" to the Barrel anymore.
Im lvl 17 Hunter, as i saw it correctly the next quest was just to return and get the reward.
I got no quests left and would like to do this one.