1217: overlay vector currupted during execution 
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    This message indicates that the overlay manager has detected an
    invalid overlay vector. The most likely cause of this is corruption
    at run time due to an invalid pointer or attempting to overlay a non
    overlayable module. Another possible cause is the use of a debugger
    to place break points in the code after an overlay vector call,
    since this replaces the vector data with a debugger breakpoint.

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