So, almost two hours to find a working solution for this error. I reinstalled everything to try to return to ADT 20, and then accidentally updated the tools and again was forced to upgrade ADT to 21, which is not suitable for me ...
The solution is to have two correct Android SDK folders, and you have to point the eclipse to another folder, apply it, it loads the SDK correctly, than you can return to the SDK that you are actually using, and everything works. Well, until the next restart and you have to do it again. Thanks to the Android developers, every new big update, new big bug in osx :)
source share