If your save becomes unreadable, boot your console into and inspect mc0:/ . Look for the directory matching your Resident Evil 4 region code. If the files inside are missing headers, delete the individual folder to clear the corrupted space, and replace it with a backed-up copy from your computer or USB drive.
Saves between NTSC and PAL without third-party conversion (PS2 Save Builder / myMC). In-game copy/loading will reject foreign region saves. Save Data Resident Evil 4 Ps2