Hi Diego,
The first line in the file should be like below fields with the lengths.
So your file should be loaded with value 640 without changing the module parameter SAPRelease if the file contain the lengths according to above table.
I think your 640 file looks good except no leading zeros for IDOC number but module is expecting leading zero's, if you add the leading zeros to IDOC number without changing anything your 640 file will be loaded successfully.
So ask your provider to send leading zero's for IDOC number in the file.
Regards,
Praveen.