Metal Gear Solid: Peace Walker

[LunaMoo]

Try default settings, reinstall the game without doing anything while it's happening or remove installation files completely, if neither of those helps, then while you might think the iso is correct, it's probably not.
Also if installation fails to install correct files aka if removing installation files helped, it's most likely your copy being corrupted/incomplete problem, such issues are typical for pirates since they commonly rip installation data from the disc to significantly decrease the file size, but in the past I think could possibly also happen to people using rewind feature or manually saving state during the installation.