If you have a teleporter stone when entering the castle, an imp 'borrows' them for awhile. They stop working if you enter without a teleporter stone (or the imp shows up the next time you try to use one), until the point you would have gotten them back.
If that is not the case, try tossing them both on the ground, then clicking on either. If they still do not work, you can place them both in a chest/barrel and download another set;
Lost Items - guide and directory of inventory files 
