Problems with an A20 safety PLC (monitor). The machine will not reset and the Jokab unit gives error code 50 (Err 50). The leaflet that came with the unit suggests switching the power off and restarting which teporarily clears the fault. The fault is listed under the heading of "CPU faults". The info in the table states "a/b twin input data diff". Has anyone got any advise or further help. The info is not in depth enough and the Jokab website is of no help.