Regarding bios display setting resolution

Hi...

I have a problem with the resolution setting in my bios.
when i set 1024x768 in the bios display setting option and passing the
kernel boot option as vga=0x317 or 0x314 for 1024x768 or 800x600,it is
booting fine.
suppose if i set 800x600 in the bios display option and passing the
kernel boot option as vga=0x314 for 800x600 it is working fine, the
problem is if i change vga option to 0x317 for 1024x768, it is not
working and i am geting an error called

Undefined mode number. press<RETURN>...<SPACE>...

What could be the probelm. please give me your valuable suggestions,

Thanks,
Robert.