I recently discovered a Dalvik error while performing the building of the project. The error message was something like:

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already added: Lcom/ ...

and:

Conversion to Dalvik format failed with error 1

Other programmers had the same problem after updating their Android SDK version and the Eclipse plugins. It seems that Google made a few modifications in the project format of an android project that change the structure and the names of the corresponding files.

The main changes were the adding of a default.properties file, the bin folder in the Eclipse tree and the use of a Library Projects folder instead of the formerly known name_src folders.

To repair your project, you have to perform the following steps.

First, you have to remove the name_src folders from the project. Do:

Right click on each name_src folder and choose Build Path > Remove from build path.

Second, you have to select the following checkbox from the popup:

"Also unlink the folder from the project"

The name_src folders will be gone from the project and the build process should work as normal.