I may be mistaken here, but I'm fairly certain that Cleric is the only class that a Ranger (Archer) can dual to. I do not believe that they are allowed a dual to Mage, Thief, or any other class. That's probably why your game crashes...it doesn' t know how to handle it.
I've never heard of anyone playing a Ranger/Mage and I'm sure lots of people would have if they could...
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Now where did I leave that doughnut?!