Frank, I spoke with a now-independent Zeiss technician about your question. Here's his recommendation: First, adjusting the sensitivity potentiometer won't help. The probe head probably "thinks" it's in a collision, causing the drives to stop.

He suggests turning the Taration ring (black knurled ring) all the way to to the right, as if you had a heavy probe cluster, and see if the problem disappears. If the problem continues, it's probably time for a service call. He suspects you have either a problem in the probe head or a bad connection between the probe head and the controller.

Hope this is helpful. Please call me at (800) 776-2388 or email to mark@cmms.com if you'd like more info.