Você precisa do Eclipse Helios (3.6.2) & acima para ADT v20 +
ADT 20.0.3 (August 2012)
Dependencies:
- Java 1.6 or higher is required for ADT 20.0.3.
- Eclipse Helios (Version 3.6.2) or higher is required for ADT 20.0.3.
- ADT 20.0.3 is designed for use with SDK Tools r20.0.3.
If you haven't already installed SDK Tools r20.0.3 into your SDK, use the Android SDK Manager to do so.