Interface Builder is unable to open documents of type CocoaTouch XIB

I just installed the laster开发者_如何学Python XCode and iOS SDK and I keep getting the following error when I open a XIB file.

"Interface Builder is unable to open documents of type CocoaTouch XIB."

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if you are using xcode 4.2.3 or newer version of then you have to no need to set HEADER SEARCH PATH. if you had added these two lines then remove it.

"$(BUILT_PRODUCTS_DIR)/../three20"

"$(BUILT_PRODUCTS_DIR)/../../three20"