The X axis had stopped working! What went wrong? I started looking at the electronics wondering if I had lost power, ground a signal, something. That was all good, then I looked closer at the stepper and noticed that the motor was turning, however the coupler had slipped off and the tie wraps were jammed against the frame stopping the threaded rod from turning.

The fix has been to grind a key into the stepper shaft and use tie wraps on the stepper shaft.