It could be a compatiblity issue. The origa chip is so outdated, I had to do a google just to find what it was and who made it. I'd recommend updating your modchip to something more recent like a DMS 4 Pro SE, Matrix Infinity, or Crystal Chip 1.1. Click the Modchip FAQ link in my sig for more info. Short of that use quality media like Taiyo Yuden or Verbatim. If that fails try rebuilding the game.
10. Q. What does rebuilding an iso mean?
A. It means that some games 4.36-4.38GB's may need rebuilt to work with Swap Magic. This isn't true for ALL games over 4.38GB's and differs on a game to game basis. The main purpose of rebuilding is to shrink the game's Table of Contents (TOC-the size of the game) in order to boot it with Swap Magic. The TOC for the Swap Magic DVD is around 4.37GB's. There is no need to rebuild games if you have a modchip. Another purpose of rebuilding is to make games run smoother. Usually the size of the game after rebuilding is smaller, but not always. Some games have dummy files used to beef up the TOC and help them run more smoothly. A good way to lower the game's TOC is to overwrite a large dummy file. If you are having trouble getting a backup to boot, and you're sure the media isn't the problem, try rebuilding the game.
Here's how to use it.. it might not work for all games though.
Open the program.
1. Select the Shrinker_ps2_psp_CdDvd5_iso.epi on the plugins drop down list.
2. Select the iso you want to rebuild.
3. Click extract LBA.
4. Click extract file and wait for it to finish.
5. Click rebuild file and wait for it to finish.
6. Click rebuild LBA.
7. Burn the new iso with Nero or DVD Decrypter as usual.