[WriteLog] Error msg. "Encountered an improper argument." received - what does it mean?

[Mike]

Keep getting an error message of "Encountered an improper argument." when
trying to get function keys to work.  What is the meaning of the error
message.  Keep getting it even though previously had been able to use the
same set-up and assigned port settings to use the function keys, etc.
without getting the error message.  WL V11.07D is used.

  73,
  Mike, K4GMH