'Defending the Dale' - "Can only have one of a unique item" message

cluster1022

Every time I accept the 'Defending the Dale' daily quest from Duvessa Shane in Bryn Shander, I get a message about only having one of a single item. I just accepted that quest from Artus Cimber in Cold Run and got the same message. I don't see any indication that they are trying to add anything to my inventory (except that message). Does anyone know what's going on there?

Note to Dev Team - how about removing whatever item this is from our inventories when we complete the quest? (I'm not a fan of unnecessary error messages...)

Thanks!!