Monitor Screen Resolution Problem Attention Out of range Screen Resolution Error message

In Linux Operating System. I change Desktop Screen Resolution.
#system-config-display or System>Administor>Display.
Here I change the Screen Resolution Display From 800*600 To 640 * 480.
While I fire the Ok Button I got the message box with
"Display settings changed

You need to log out and restart the X server for the changes to take effect.

Configuration was written to /etc/X11/xorg.conf, original configuration saved as /etc/X11/xorg.conf.backup."
PROBLEM:
After I restart the System while starting the Graphical window I got the following error message.
Attention
Out of range
H:106.1KHz V:84.9Hz
SOLUTION:
1)After I restart the system the modified screen resolution 640*480 it does not support monitor.So that I got the error message "Attention Out of range".
2)Then I go the directory /etc/X11.
3)Here System main take the backup copy of the old screen resolution configuration file form /etc/X11/xorg.conf to /etc/X11/xorg.conf.bakp
4)I rename backup file #mv /etc/X11/xorg.conf.backup /etc/X11/xorg.conf
5)Restart the system Then try it The problem will be resolve. If you still face the problem  go to the #system-config-display or System>Administor>Display. and change to the old setting.