User-Defined PLC Function Error

What does E.16 to E.20 mean?

The inverter output is shut off because a user-defined protective function, configured via the PLC function, has been activated. This occurs when a value between "16" and "20" is written to the special register SD1214 while the PLC function is enabled (Pr.414 is not "0"). It signifies a condition that the user's PLC program has flagged as a fault.