xrandr not working in dual monitor

Hi ,

             I am not able to change the resolution of the Monitor
dynamically at runtime after staring X.

       i tried with xrandr command its giving error 

"Xlib extension "XRANDR" missing display ":0.0".      "

          I am attching my XFConfig file. In XFree86.0.log it shows
"RandR enabled "
.......
RandR .....     Initializing etc.
              

             And if i disable Xinerama xrandr is working. Is it that
Xinerama and XrandR doen't coexist or what ?

Karthik