1203: file <filename> is not a valid .EXE file
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 This message indicates that the specified file does not have a valid .EXE
 file header, thus the Blinker internal overlay cannot be located within the
 file. This indicates that the file has become overwritten by another file,
 that the PATH has changed so that an alternative file of the same name is
 found instead, or that the .EXE file has become corrupt.

 Try recreating the .EXE file, using external overlays (via the SECTION INTO
 xxx command), and marking the .EXE and .OVL file(s) read-only.

 Note: The Blinker errors 1201 through 1204 can occasionally result from the
 effects of a virus, so if the above measures do not help then perform an
 extensive check for viruses and take the necessary measures for removal.