Hello there. Many of you who have installed Kubuntu KDE4.x version along with Ubuntu or who are using a standalone installation of Kubuntu may have come across this annoying error “Compositing has been suspended by another application. You can resume using the ‘Alt+Shift+F12’ shortcut” even after installing proprietary graphics drivers . This error can be fixed in three steps (thanks to ubuntuforums).
1. Click the start button ans select System Settings
2. Go to Desktop -> Desktop Effects -> Advanced
3. Tick Disable Functionality Checks and click apply to save change.
Thats it. Enjoy the Kwin Compositing .