Lirr M3 Door Control Issues

I've been having problems controlling the doors on the M3. At some stops the Tab key controls work fine. At other stops, the doors will not open. The door control key appears and it is in "Doors Comm" position. The "Unlock rear doors". and the "Lock rear doors" buttons continually move in and out. Why am I loosing door control in the middle of a run?

 

Make sure the brake is at least 50% applied.

 

Ahaa!!! It works! Thank you