On building the project in XCode with Cocos2d framework I am getting the following error.

dyld: Symbol not found: __NSConcreteStackBlock

Answer

If you use blocks anywhere in your application, you'll see a crash similar to this on a pre-4.0 OS while building with the LLVM compiler. To work around this, you can specify the linker flag -weak_library /usr/lib/libSystem.B.dylib in your Xcode build settings.