XCode 4 - Errors building project with undefined symbols for architecture

I'm getting the following build error and I have no idea why. Any help would be greatly appreciated. I'm not entirely sure whether I'm missing a particular framework or not.

Undefined symbols for architecture i386:
  "_OBJC_CLASS_$_YAJLParser", referenced from:
      objc-class-ref in libem.a(EMDynamicBrandController.o)
      objc-class-ref in libem.a(EMDynamicKeywordsDataSour开发者_运维技巧ce.o)
      objc-class-ref in libem.a(EMURLEndecaSearchResponse.o)
ld: symbol(s) not found for architecture i386
collect2: ld returned 1 exit status

Thanks in advance.

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I ended up using and including the following Framework and it now builds successfully:

YAJL Framework

The YAJL framework is an Objective-C framework for the YAJL SAX-style JSON parser.