/sys$common/syshlp/helplib.hlb UIL, Compile Time Errors, BACKSLASH_IGNORED  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  ERROR:  A backslash was followed by an unknown escape character.   \
  is the escape character in UIL.  A selected set of single characters
  can follow a \ such as \n for newline or \\  to  insert  a  \.   The
  character following the \ was not one of the selected set.

  USER ACTION:  If you want to add  a  backslash  use  \\.   Otherwise
  consult the documentation for the supported escape sequences.