Fixed the issue when trying to access submodules:

$ git submodule update --init --recursive
fatal: reference is not a tree: b51de15acb37d72719b03314771e4caa04e57a33
Unable to checkout 'b51de15acb37d72719b03314771e4caa04e57a33' in submodule path 'CocosBuilder/libs/cocos2d-iphone'

There is a multi-step process in order to make this work (detached HEAD) with the latest for tag “release-1.1-RC0”