This is a very common issue for PSP saves. It usually points to a mismatch between the save file's region and your game's version.
On the PSP, Test Drive Unlimited uses the system's standard save functionality. You can save your progress through the in-game menu, which will create a single, fixed save file that records your entire career, garage, and house purchases. To ensure this process works without issue, your PSP's firmware must be updated to version 2.0 or later.
If you later want to revert to your original save, simply delete the new save folder from your SAVEDATA directory and copy your backed-up folder back in its place.
Even when following the guide, problems can occasionally arise. Here are some common issues and their solutions:
