I am also having this problem. It has something to do with the loot window being unable to open. Something in the game probably keeps trying to but can't because when you try to reactivate the container to obtain the item it gives a "This is already being used" message.
I think this only applies to specific containers because I have no problem looting drops from mobs. I will try to open a chest and see if I get this problem for that as well. Real pain the ass because it makes some quests (in this case a class quest) impossible to complete.
Yea, having the same problem as you. I can't take the book that is required for the quest from the bookshelf eaither. Therefore I can't complete the quest and I could really use the weapon I get from the Quest.
Scrow, Nostalrius has a BugTracker for these issues. You can find the link in my signature. It's easier for the Developers to keep track and fix bugs when you add the issue on there.