How have you wired the probe? On the Galil, we use the latch inputs. Input 1 = X, 2 = Y, 3 = Z, etc... If your Z axis is Galil axis 3, then the probe needs to be wired to input 3. Also, the DIGITIZE signal needs to be mapped to the input #3's pin number. All this is fine if all you want to probe is Z moves. But if you want to do X, Y, and Z, then the probe needs to be wired to inputs 1, 2, and 3. Then you need a brain to set DIGITIZE signal based on if either input 1, 2, or 3 is high.
Steve