Sorry dude I misread your post. Physically look in your Mage Spell book to make sure that you definitely have spells memorized. Silly as it seems but check to make sure you're not wearing a cursed item or the like which has dropped your intelligence below that needed to cast spells. Finally, I guess it's not possible to dual to a mage if your int' was too low to begin with, but it may be an int' problem so check your stat's. Come back on this Nazgul, it's interesting.
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It's bleedin dark down here, slippery too.

Man, that's a pisser.