Vista - External display resolution reset everytime I logon or unlock

I have an HP 6510b notebook with Intel 965 Express Chipset Family display
adapter and I use and external monitor to "extend the desktop" (I use both
internal and external monitors). Both the monitors work properly except the
resolution reset issue on the external monitor.

Whenever I logon to my account or unlock my notebook, the resolution on the
external monitor is reset from 1280x1024 to 800x600. This is quite annoying
as I need to unlock or logon to my account several times a day and each time
I unlock or logon I need to adjust the resolution.

I have the latest Intel drivers and Vista patches installed in my notebook.
Can somebody help what the problem could be?