Is It Safe To Apply 24V Across a 12V Motor?
Ok, a couple of things:


It's pretty much never a good idea to surpass recommended brushed DC motor voltage ratings, as doing so will definitely damage/overheat your motor leading to safety issues.
If you need to increase your power/torque, the way to do that is to add another motor controller/motor and in your code set them to be equal/inverse.
I've worked with that motor before, and it definitely should not be drawing >60 amps, even 40 amps is alot.  Try using a multi-meter to test current, or put in a 40amp fuse in series with your motor wiring.
What motor controller are you using?  Considering you're using a CIM I assume it's FIRST (Talon, Victor, Jaguar, etc).  If you motor was drawing over the maximum current you would not get an "error," rather it would simply stop working.  I recommend revisiting your wiring diagram.  Additionally, these motors draw a lot of current, make sure your power supply can handle them.


I would love to hear more about your project so I could better understand your issue.