Comment 3 for bug 509329

I have an identical problem with a laptop with a radeon xpress 200M graphics card running lucid using the radeon driver. The system boots to 1024x768 on both screens. Trying to change the screen settings with the gnome-display-properties applet allows you to put the laptop screen to native resolution, but trying to change the settings of either the laptop or external screen to anything other than 1024x768 makes the external screen go blank. (and it flashes up "no signal")

xrandr also reports that the external screen native resolution is 1360x768 (60Hz), but trying to set this resolution manually with xrandr results in the same blank screen and "no signal" message.

I also booted into Windoze and the laptop and external monitor work fine both at native resolution.

I'm happy to provide debugging info if requested.