1217:   overlay vector corrupted during execution

     Explanation:  This message indicates that the overlay manager has
     detected an invalid overlay vector.  The most likely cause of this is
     corruption at runtime due to an invalid pointer, or an attempt to
     overlay a non-overlayable module.  Another possible cause is the use of
     a debugger to place breakpoints in the code after an overlay call, since
     this replaces the vector data with a debugger breakpoint.

     Action:  Use of the MURPHY command for debugging overlays may help
     to identify whether non-overlayable modules are responsible for this
     message.