Assuming you’re using Xcode 4, it’s likely that the dependency checker is confused because there are .h files in list of C files to be compiled.
So…. Navigate to your target’s “Build Phases” tab. (Click on the project, then click on the target’s name, then click on the “Build Phases” tab.)
Ensure that you didn’t drag any .h files into the “Compile Sources” section.
It’s common, when importing code, to just drag the whole lot into that section, not realizing that .h files aren’t technically compiled, and the dependency checker isn’t smart enough to spit out more helpful error message.