“Conversion to Dalvik format failed with error 1” on external JAR

Question

In my Android application in Eclipse I get the following error.

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already add

Answer 1

In general, it seems that this problem comes when there are unnecessary JAR files in build path.

I faced this problem while working on IntelliJ IDEA. For me it happened because I added JUnit and Mockito libraries which were being compiled at runtime. This needed to be set to "testing" in module properties.