Please this will be not DUPLICATE question
Don\'t know but I have already put .jar in libs folder and also done following process
I had the same problem. The dropbox-sync-sdk-android.jar was existed on the class-path, but the classes were not included to resulting apk during build process. Later I noticed multiple errors in Android build console:
[dx] bad class file magic (cafebabe) or version (0033.0000)
Looks like Dropbox API is compiled against JDK 1.7 and you will have troubles when trying to build APK with this jar using JDK 1.6
I fixed this issue by updating Compiler compliance level:
Project->Properties->Java Compiler->Compiler compliance level->1.7
Also make sure that your Android SDK Build-tools are v19 or later:
Android SDK Manager->Android SDK Build-tools->check v21.0.2->uncheck v17(my case)