This is on an Asus EeePC 900, with the following video hardware:

00:02.0 VGA compatible controller: Intel Corporation Mobile 915GM/GMS/910GML Express Graphics Controller (rev 04)
00:02.1 Display controller: Intel Corporation Mobile 915GM/GMS/910GML Express Graphics Controller (rev 04)

It has a built-in 1024x600 screen.

I normally have a 1280x1024 external LCD monitor on the VGA port,
which i usually set up with:

  xrandr --output LVDS1 --mode 1024x600 --output VGA1 --mode 1280x1024 --above LVDS1

However, I was experimenting with panning, and now the above command
fails with the following message:

0 dkg@pip:~$ xrandr --output LVDS1 --mode 1024x600 --output VGA1 --mode 1280x1024 --above LVDS1
xrandr: Configure crtc 1 invalid time
1 dkg@pip:~$

To get it to work as expected, i need to explicitly turn panning off
and then try again:

0 dkg@pip:~$ xrandr --output LVDS1 --mode 1024x600 --panning 0x0 --output VGA1 --mode 1280x1024 --above LVDS1
0 dkg@pip:~$ xrandr --output LVDS1 --mode 1024x600 --output VGA1 --mode 1280x1024 --above LVDS1
0 dkg@pip:~$

After the first command (with --panning 0x0), LVDS1 was still showing
as though it was --same-as VGA1.  I had to run the second command to
make the --above actually take effect.

So there is some weird persistent panning interaction going on.  and
at the very least, the error messages could be improved.

Regards,