This is a common error when converting a older project to Swift 2.x in Xcode 7 (though you might see it in other conversions, too). Specifically, I frequently see this error in the tests target when opening old projects:

This is often a result of incorrect value in the "Framework Search Paths" of the tests target:

If you remove the string in that "Framework Search Paths" for the appropriate target, that error will go away. For some reason, Xcode doesn't generally introduce this error in the main target, but only the tests target.
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As an aside, when opening up an old project, it's good practice to select the target and then choosing "Validate Settings..." from the "Editor" menu. A lot of cryptic error messages will be resolved when you do that.