You have to include two more things:
#import "GAIDictionaryBuilder.h"
#import "GAIFields.h"
Checking what’s in GAIFields.h I can see that kGAIScreenName is there:
extern NSString *const kGAIScreenName; // synonym for kGAIDescription
Might be important point that the current Google Analytics is in beta, so using the latest downloadable SDK is always a good idea. What I tried and what is working currently for me is Version: 3.0 (August 16, 2013).