Unknown type name 'namespace' in Xcode 4.2

I suspect the translation is C or Objective-C, where namespace is not a keyword as it is in C++ and Objective-C++.

Another possibility is that a previous header did not close a body (e.g. forgotten }; at end of class declaration of forgotten } at end of function definition).

You can rename your file with .mm or you can select your .m file and change the "File Type" to "Objective-C++ Source".