Go to Project "Properties" Java Build Path "Libraries and delete everything except" Android XY "(in my case Android 1.5). Click" OK. "Go to Project" Clean "Clean projects selected below" select your project and click "OK". That should work.
It is also possible that you have a JAR file located somewhere in the project folders (I copied the Admob jar into my src forlder) and THEN added it as a Java path library. It does not appear in the package explorer, so you do not notice it, but it is counted twice, causing a terrible Dalvik 1 error.
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