That's strange. This is what works for me with other people's rosters:
1. Create a NEW roster save in-game.
(Details: Don't edit anything; just use the game's default rosters. Start the game and go to Rosters, Save/Load, Save. Name it anything you want.)
2. From the PS3's menu, copy your new roster save to a USB stick.
(Details: Go to "Saved Data Utility". Go to the roster file that you just created. Press triangle, and select COPY. Select your USB drive.)
3. Plug the USB device into your computer and navigate to the save files.
(Details: On the USB drive, open the PS3 folder. Keep opening its subfolders until you find the save files.)
4. Overwrite the old "USR-DATA" file with the new one from my upload. Leave all of the other files alone.
5. Go back to the PS3. Go to "Saved Data Utility" and find your USB Device. Copy the files back.
Let me know how it goes. More feedback from others would be appreciated, too.