What would cause the PRG characters to flash on the central display of a TSX 37 Micro?

The 'write protect switch' set in the 'write authorized' position will cause the PRG characters to flash on the central display of a TSX Micro.

Note: The TSX37 is obsolete and it is recommended to upgrade to the M340 with the x80 I/O contact locals Schneider Sales office or Distributor for more information.