After connecting Eclipse Android project up to Team Foundation Server the application the following error occurred:
Conversion to Dalvik format failed: Unable to execute dex: null
After doing a Project -> Clean the problem got solved.
If this does not solve it. Try look in the bin folder of your project directory and you will see .dex files generated. Delete them and try to run your project again. Third option is to remove the project from your workspace and then import it again.