Right Click on your project -> Build Path -> Configure Build Path -> Order and Export Tab.
Make sure that "Android Private Libraries" is checked for Export.
If you've added any libraries from the libs/ folder, remove them as they are automatically added in the "Android Private Libraries" section.
Or try this : https://stackoverflow.com/questions/16596969/libraries-do-not-get-added-to-apk-anymore-after-upgrade-to-adt-22
Right Click on your project -> Build Path -> Configure Build Path -> Order and Export Tab.
Make sure that "Android Private Libraries" is checked for Export.
If you've added any libraries from the libs/ folder, remove them as they are automatically added in the "Android Private Libraries" section.