Those resolution errors are caused by something else. Likely your monitor doesn't support Edid for reading out resolutions. To remove these errors add the following line to your device/screen section of your XF86config-4 file:
Option "IgnoreEdid" "1"
Then those errors will be gone, but those errors aren't "crashing" X. It were only errors meaning that the drivers couldn't verify if the resolutions are supported by your monitor. Because it couldn't verify any mode it used:
(**) NVIDIA(0): Default mode "800x600": 56.3 MHz, 53.7 kHz, 85.1 Hz
(II) NVIDIA(0): Virtual screen size determined to be 800 x 600
The real error is somewhere else. Can you paste the rest of your Xf86Config-4 file?