nib file not opening in Xcode 4

I am trying to move from xcode 3.1 to 4.1 and in the process, I installed Xcode 4.1 and opened project I开发者_运维技巧 created with Xcode 3.1. But when I build project, it gives error:

The document "filename.xib" could not be opened. The operation couldn’t be completed. * -[NSCFArray insertObject:atIndex:]: attempt to insert nil.

The file is not full screen View with status bar, it is freeform view.

Thanks, Jignesh

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Try this: goto XCode Menu => File => Add Files to your-project, a finder-like browser will pop up. Navigate to your Classes directory. Do you see the filename.xib and can you click on it? Then add it to your project.