I spent a few hours yesterday homing the machine and testing all the limits over and over again. I did notice that after the machine homed the machine position would register .0191 for B axis not Zero. I called the dealer I got the machine from last year and they suggested I Shut the machine off and power it up holding the "P" ( which is also the "O" ) and "Cancel" buttons down while the computer boots. It worked. I homed the machine and all axis Zero'ed correctly.
I did'nt stop there though. I checked the limits over again and would sometimes get that .0191 error again. It I believe is the amount of B+ axis over travel which the parameter is set to 500 ( 1/2 a millimeter). So I think maybe that the software limit is too close to the home prox sensor. I'm going try mudracers advice and increase that limit to 1000 like it is set for the x and y axis ( and watch it closely). Most likely the the coupling slipped a little on the Ball screw, ( the screws on it weren't very tight).
I had a similar problem to Lyfordln with a Bridgeport 760Vmc z axis homing some times off by a revolution , and it was that the homing proximity switch was too close to the timing mark on the encoder. All it took was moving the trip dog a little so it would hit the switch aprox 180 degrees from the timing mark on the encoder.
Thanks for the replies