Xcode "Build and Archive" button disabled for Mac app. Why?

I am buil开发者_Go百科ding a Mac app, but the "Build and Archive" menu item is disabled. I am running Xcode 3.2.4 and OS X 10.6.5. Any suggestions?

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Download and install the "Application Tools" package fixed it for me.

Links to the Application Tools download can be found on the index page for the Mac developer program.