As noted in the newly posted Lets Play series on the Tutorial chapter the tutorial doesn't actually highlight valid items to drop, un-equip, or equip - despite the rest of the tutorial highlighting buttons really well. Probably because there's no guarantee valid items are present since the player can drop too much or something.
Maybe we can for the tutorial disable non-highlighted options so you can't get stuck in a bad state.
http://steamcommunity.com/sharedfiles/filedetails/?id=734348436