My app used to work perfectly fine. Recently I updated eclipse (the plugins), and now I am getting this error. I have not changed my code so I know it should continue to work. but it does not. I am using the google eclipse plugin, which the updates changed to version 8.
Basically I still see everything in the android project. the gcm.jar is still there for example. And my manifest has not change. I can keep listing stuff but it would just be more words. Bottom line: It used to work fine.
Just adding to @athor's answer, as you said that you updated everything. Its a high possibility that you updated android SDK-tools to latest version 22. This is a known issue and this has been discussed many times. You might want to check out following threads and picture.
Android app crashes after SDK-tools update version (NoClassDefFound, tool version 22)
ERROR : java.lang.NoClassDefFoundError: android.support.v4.content.LocalBroadcastManager
The picture and thread will help to find the exact location where to make changes. Hope this helps.