If you configure the CREATE_FILE, OPEN_FILE, WR_DATA_TO_FILE and CLOSE_FILE to create or open a file on the M340 or M580 data storage SD card,  attempts to perform either a write to the file or close the file without properly considering the usage of the FILEDESC output on both the CREATE_FILE and OPEN_FILE blocks  , will results in an error 21 getting returned..
This is due to the output of the OPEN_FILE block over writing the output of the CREATE_FILE block.
To resolve the issue, the following logic can be used as an example on how to configure the OPEN_FILE and CREATE FILE.
Released for:Schneider Electric Canada