[SOLVED]""required virtual size does not fit available size: requested=(2304, 768), minimum=(320, 200), maximum=(1280, 1280)""

Platform:
                 Ubuntu 11.10(or other releases, not sure)
Diagnosis:
                 Unable to set up dual(multi)-displays, with an error message like ""required virtual size does not fit available size: requested=(2304, 768), minimum=(320, 200), maximum=(1280, 1280)""
Solution:
                 Modify /etc/X11/xorg.conf file, to set the "Virtual" parameters properly.
                 sudo vim /etc/X11/xorg.conf
                 Locate section "Screen", create a subsection "Display" with a parameter "Virtual" with the values indicated as required in the error message, e.g. 2304 and 768 here.
                 Subsection "Display"
                ... // other parameters if any

               Virtual 2646 1024
         EndSubsection

                  Log out and log in, go to "Displays...", uncheck "Mirror displays", apply.