VMS Help UIL, Compile Time Errors, CONTROL_CHAR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  ERROR:  The compiler encountered a illegal control character in  the
  specification  file.   The  decimal  value of the character is given
  between the \ \ characters.

  USER ACTION:  Replace the character with the sequence  specified  in
  the  message  (for  example, \3\ if the control character's internal
  value is 3).  UIL provides several built-in control characters  such
  as  \n  and  \r  for  newline and carriage return.  Consult the "VMS
  DECwindows User Interface Language Reference Manual" for a  complete
  list of supported escape sequences.