I get the message when trying to go into fullscreen mode. It tells me:
Switching to Fullscreen mode: Display mode 864 x 480 not supported, switching to next best 1024 x 768.
I'm pretty sure I've used that resolution for something on my computer. I'm currently getting the Lost Planet demo just to see if that supported it.
Edit: Nevermind, I guess I haven't seen that resolution seen anywhere.