You do NOT need to reformat the hard drive!
I previously had a few "Corrupted Data" icons on my PS3 for many months. I got an error message every time I attempted to delete these files, but I finally found the solution. There is no need to back-up any files, but you can if it'll help you feel better. I've shared this trick with many people, and there were no problems. Don't hold me responsible if you lose anything, though. Just follow these steps...
1. Turn off Playstation 3.
2. Hold the power button down; the system will turn on and turn off once again.
3. Once the System has been shutdown, re-press you finger until you hear 2 consecutive beeps
4. When you hear the 2 beeps take finger off power button.
5. You will be prompted to plug in your controller via USB and then hit the PS button.
6. The Recovery menu will pop up.
7. Select "Restore File System" from the Recovery menu.
8. Agree to restoring the file system.
You'll see a progress bar detailing the restoration, and once it is finished your system will restart. Your "Corrupted Data" icons will still be there, but you will now be able to delete them. :)