A DAC overflow means the control sent commands to move an axis but did not see movement. Either it did not move or did move and the encoder count is not being seen by the control.
Based upon what you did, it seems the drive is not receiving a command to move. A open armature cable would give you a axis drive fault.
Either a bad connection in the command line or a lack of output from the BMDC.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)