After googling around, the problem is simple enough: Some properties are f* up when transfered from older Xcode to newer Xcode. What I did to fix this is to go to the project settings, and find Base SDK. It was set to ppc_something, and Xcode 4 does not support those SDK. You have to convert it to the newest one. I set it to 10.6 to be safe in the future.
Probably its just because I downloaded a very old code. But its from Apple official website, so they should give a warning or s**t!