I did do that for both C and C++, although I do not use C++. It had no effect. I think the important part is there is no such setting in the Objective C section. Two files, in particular, use the .m extension and I assume that invokes the Objective C compiler. Both files include the same problematic header files. If I compile them individually using the Build/Perform Action menu then one succeeds and the other fails. The one that succeeds has no Objective C objects coded. It does reference OS objects like NSArray, NSData. The one that fails has Objective C classes and objects that I coded. Does the Objective C compiler have different paths of compilation based on the contents of the file? Could that lead to different implications of the C Processor? Note that the header includes are right up top in both cases.