VMS Help MACRO, VAX MACRO Assembler, Directives, .ERROR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Causes the assembler to display an error message on the  terminal
    or batch log file and in the listing file.

      .ERROR [expression] ;comment

    expression

    An expression whose value is displayed  when  .ERROR  is
    encountered during assembly.

      ;comment

    A comment  that  is  displayed  when  .ERROR  is  encountered
    during assembly.  The comment must be preceded by a semicolon.