Today I upgraded to Android SDK 2.3 and I also upgraded the Eclipse Plugin Androi Developer Tools 8.0 (from 0.9.9). I also upgraded my Java Development Kit to 1.6_22.
i have also encoutered this and solve it by changing the android choice in project properties. My error is because the project can't find proper lib from the android SDK. Then fix the project using android fix tool in right click of project, clean it and then correct.