CAL FAIL - Unit will not enter Cal mode

Unit reads cal fail on both sides. We have already checked batteries, jumper, wire to power supply and fuse. We cannot get the unit to enter cal mode on startup (holding both + and - buttons on the Second Cuff pressure adjustment while powering on). The unit goes through its self-test while powering on, then displays the failure. As background, the error message first appeared right after we had begun a calibration on the unit. We have been unable to get the unit to do anything else since.