Screen Resolution stuck at 640x480 after installing Bumblebee

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http://askubuntu.com – I have a Dell XPS 15z laptop. As you can see here, there are some issues with NVidia drivers. The site recommends installation of Bumblebee (instructions given in the link). I am posting it again for ease: $ sudo add-apt-repository ppa:bumblebee/stable $ sudo apt-get update && sudo apt-get upgrade $ sudo apt-get install bumblebee bumblebee-nvidia $ sudo usermod -a -G bumblebee $USER After restarting the computer however, the screen resolution was stuck at 640x480 and I got the following error message as soon as I logged in: **Could not apply the stored configuration (HowTos)