Xvfb failed start error

I have Ubuntu 11.04 I am trying to install Xvfb and CutyCapt in order to take a snapshot of webpage I followed a instruction https://github.com/jaequery/cutycapt-installer-script-on-ubuntu/blob/master/install and I executed last line and it gives me an error xvfb-run: error:Xvfb failed to start Any solution for that? Thank you in advance