Why is this resolution "inaccessible"?

[Mikael Eriksson]

On Thu, Jan 19, 2006 at 11:08:12PM -0500, Alex Deucher wrote:
> If you are using the intel hardware you are limited to what modes the
> bios knows how to program.  if it doesn't have a 320x240 mode you are
> out of luck (unless you use the various i8/9xxreolution, and
> replacemode tweaks.

% sudo 855resolution -l
855resolution version 0.4, by Alain Poirier

Chipset: Unknown (id=0x25908086)
VBIOS type: 2
VBIOS Version: 3412

Mode 30 : 640x480, 8 bits/pixel
Mode 32 : 800x600, 8 bits/pixel
Mode 34 : 1024x768, 8 bits/pixel
Mode 38 : 1280x1024, 8 bits/pixel
Mode 3a : 1600x1200, 8 bits/pixel
Mode 3c : 320x240, 8 bits/pixel
Mode 41 : 640x480, 16 bits/pixel
Mode 43 : 800x600, 16 bits/pixel
Mode 45 : 1024x768, 16 bits/pixel
Mode 49 : 1280x1024, 16 bits/pixel
Mode 4b : 1600x1200, 16 bits/pixel
Mode 4d : 320x240, 16 bits/pixel
Mode 50 : 640x480, 32 bits/pixel
Mode 52 : 800x600, 32 bits/pixel
Mode 54 : 1024x768, 32 bits/pixel
Mode 58 : 1280x1024, 32 bits/pixel
Mode 5a : 1600x1200, 32 bits/pixel
Mode 5c : 320x240, 32 bits/pixel

Note that I have not used 855resolution to changes the modes.

And yet Xorg.0.log says:
(II) I810(0): Not using mode "320x240" (no mode of this name)