I cannot move the robot up or down during training (Z-axis)

During training its not possible to move the robot up / down (Z-axis), but other directions are possible? 

Please check at first the correct wiring of the sensor and the cable for damages. 

Then check the status of the sensor in the web interface, does the message "Faulty 4096" appear there or is the status not "Good" ?

Then an update of the Computebox as well as the sensor can help. You can find the instructions here

Please perform an additional calibration of the sensor after the update. 

After the update the status should change to "Good" and the guiding should run error-free again.