XCode Unit Test Target problem

I made my first attempt tonight at creating a unit test target for a Cocoa project in XCode 3.0.  I followed the instructions in the UnitTesting.pdf from the Apple Developer Connection website.  I believe that I did everything laid out in the document but when I go to build the unit test target I get a build error .....

Building target “RankerTestTarget” of project “Ranker Rev. 0” with configuration “Debug” — (1 error)

i686-apple-darwin9-gcc-4.0.1: /System/Library/Frameworks/Cocoa.framework/Headers/Cocoa.h: No such file or directory

i686-apple-darwin9-gcc-4.0.1: warning: '-x objective-c-header' after last input file has no effect

i686-apple-darwin9-gcc-4.0.1: no input files

Build failed (1 error)

It looks like the critical item is that it can't find the Cocoa.h file.   Has anyone experienced this problem.  The .pdf file was written in in '05 so I am suspecting something has changed since.

Thanks