@ZakariahMT It could just be the ribbon cable between the Duet and Duex is damaged, or one of the wires is making intermittent contact; have a good look at it. That would cause random driver errors, and possibly for the drives on the Duex to not enable. Plug it into the Duet and Duex, then measure resistance across the ribbon cable by testing at the pins on the back of the board. Check all the pins are soldered properly on each board too. There isn't much to go wrong on a Duex!
Are there any heater or motor wires running close to the ribbon cable? It can be susceptible to interference.
Ian