He couldn't because jkk put interiors in the WRONG FOLDER.
Just go into the .mis file and find the InteriorInstance. after you've found that, you should see a folder path? Remove the addon/ and it should work.
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The actual level was ..kinda meh. The level picture wasn't even a picture, it was pretty unreplayable and overly linear. If you could've found a way to incorporate shortcuts, and while you're at it got rid of the tightropes, this wouldn't be bad.
EDIT 2: The PT was way too high, I got 16.8x the 2nd try on the level.
EDIT 3: Your link in the first post is broken.