Maybe it has file errors? To check and fix those, connect your PSP to your PC via USB. In Windows Explorer right click the PSP drive [e.g - drive E:], go to Properties, select the Tools tab and in the the Error Checking section, chose Check Now. Select your options in the dialog box that appears and click Start. The process should correct the errors.
If that does not work, try formatting the memory card. Be sure to back up the contents of it first before doing so to avoid losing data.
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