.ERRDEF          Error If Name Is Defined                      MASM Directive

  .ERRDEF   name

    Forces a fatal error if name is defined.

       Notes:     If the name is defined as a forward reference, it is
                  considered undefined on the first pass, but defined on
                  the second.

                  The error message that may be generated by this
                  directive is 'Forced error - symbol defined', which is
                  error number 93.

                  If an error is generated, the object module is deleted
                  and the assembler exits with an exit code of 7.