3.80 M33-5 SaveData

Okay, so I finally upgraded to 3.80 M33-5 after my friend pestered me about for days on end. I was originally playing Metal Gear Solid: Portable Ops Plus on 3.40 OE-A, and now, for some reason, my save file is displayed as corrupted. I know the file hasn't actually changed, since I backed it up on my computer, so how do I make it start working again? I made a new save file to check if any worked it all, and only the ones created on 3.80 M33-5 seem to work. My guess is that something in the 3.40 Kernel that it required was lost in 3.80 M33-5, but I'm not exactly knowledgeable about this stuff.

Any help would be greatly appreciated.