Unable to run the motor in reverse direction (AX2550HE)

I'm controlling an AX2550HE via RS232. I'm able to run the motor (a DeWalt 24V drill) in one direction but not the other. For example, !A7F works great, !a7F does not. The LEDs in the front indicate that the controller is going in reverse, however, when I measure the voltage across the motor I get 0 V. Why is the unit not putting out voltage in reverse?

There is no reason why it would work in one direction and not the other.
Try operating the controller with the PC utility and check that nothing looks unusual or different when you move the slider in one direction vs. the other. Verify that you see the power out graph moving as you move the slider. Verify that there is no battery voltage drop below 11V (battery voltage and internal voltage) as you go in the reverse direction.
Note that one possibility for the problem can be if you connect the motor to one wire from Ch1 and to another wire from Ch2. Check the wiring carefully.

I'm really embarrassed - you were exactly right about the wires, I had accidentally used a color from each channel to the motor. I wired it correctly and it works great.