Library /sys$common/syshlp/BASICHELP.HLB  —  Run time errors, ILLRESSUB
  Illegal RESUME to subroutine (ERR=247)

  While in an error handler activated by an ON ERROR GO BACK, the  error
  handler  attempts  to  RESUME  without  a line number or a label.  You
  cannot RESUME to a line or label in any program module except the  one
  containing  the  error  handler.   This error cannot be trapped with a
  BASIC error handler.
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