I just tested a shield scroll on an item and it worked for me.
While I am not saying that there is no bug in your situation, unfortunately there is a lack of supplementary information provided here which may help the Staff or other players in reproducing such an error - thus making it harder/impossible to fix.
I would recommend you to also make sure the item has remaining enhancement slots, if a shield scroll is still unable to be used then maybe a few screenshots of the error message and IF the shield had been consumed in this process or not.