Platinum Save Backup problem.

[ninty_g]

Hi I have a problem backing up my platinum save, I can back up the save successfully using the 3in1+ backup tool but when I back it up the save is 256 kb I tried loading it up with that size and I also tried changing the size using the sticky in this forum with a tutorial on how to fix the size, but either way when I load it up it claims that the save file has been erased due to corruption or damage, so whats the problem? I know my save isn't corrupted because my platinum works fine and loads up the save fine so what could it be?