Android App isn't installed issue

I upgraded to Unity 5 and recompiled my game and executed to my device just fine. After editing the android manifest I am stuck with this issue:

Unity generates the APK, push into device but never executes it , then i manual tap to open the game and i get this message "Android App isn't installed"

I had a backup of the original manifest before editing. So I replaced the modified file with the backup, but the app still doesn't open !!!

Any help is highly appreciated.