Error opening file - Staff.fmt

That error means something is definitely wrong with your pack file - it's unable to load the 2d art of that staff your templar has.
Have you tried the Pack Check, and other suggestions noted in this thread?

If you had the gems in that hammer item, they'll stil be it, unless you threw it away/sold it, but you can't do that without a warning there are gems in the item.
Did you perhaps leave the hammer in your other weapon set? You can hit 'x' to weapon swap to the other set to see if it's there.