Ensure your "ISO Mode" is set to Inferno or NP9660 in the PSP VSH menu.
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The "UPD" version is still shared on archive sites because PPSSPP users found that the original ISO has a memory leak during 6-man matches. The patched "UPD" ISO reduces the chance of the emulator crashing during the Royal Rumble. Ensure your "ISO Mode" is set to Inferno