iPhone "_OBJC_CLASS_" compilation error

I am trying to compile my project in Xcode. But i am getting the following error.

 "_OBJC_CLASS_$_InfrastructureBenchmarkingViewController", referenced from:
  objc-class-ref-to-InfrastructureBenchmarkingViewController in RootViewController.o

4 more of similar type.

Can't understand the meaning of this error?

Small Clarification: Actually the _Infrastructu开发者_开发百科reBenchmarkingViewController was a module in another project. The files pertaining to that I have copied into the new application.

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Sometimes it happens when the project definition file (.xcodeproj/project.pbxproj) is somehow messed-up, eg. because of XCode crash or project is taken from someone else, etc.

So try removing InfrastructureBenchmarkingViewController (Delete the file, then choose "Delete reference", so it is not deleted physically from disc) and then again add this file to project (Add > Existing file from the project context menu).

It worked for me several times.

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you need to link in whatever framework _InfrastructureBenchmarkingViewController is a part of. Try going to the project window, right click on frameworks and choose add existing framework ....

you should be able to find the framework including _InfrastructureBenchmarkingViewController there.

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Seems you have some object files that are not valid anymore. Use the clean option from menu and build it again. That should solve it.