I am rather new to cocos2dx and I am trying this version. I had exactly the same problem.
And I am able to add the NDK include path in the C++ include paths, although I am not sure about the cocos2dx include path, but after a search in the file system I include it at: $(COCOS2DX_ROOT)/cocos/2d
But after this, despite the disappearance of include error, Symbol 'cocos2d' could not be resolved is reported in the "using namespace cocos2d" statement.
I have to it is not as easy as it seems/claims to get everything work. In fact it is quite frustrating during the whole process. I have been struggling set it up for quite a few days. At first I tried the cocos2dx 2.2.3 by following a post in the forum and other online documents. Everything was almost done until I opened Eclipse, when it repeatedly complained errors, I fixed several ones based on the error log. However there is one I cannot fix and even after I Google it, I still cannot figure it out.
So I now am trying cocos2dx 3.0rc. In fact it works much smoothly when I work it on command line. Now the only problem left is this symbol not resolved one.
Please can anyone help?