I have been plagued with this for several months now and still have been unable to get rid of it.
Anytime I play certain games (Need for Speed: Most Wanted, Shattered Galaxy, Atlantica Online, Shot Online, Pangya to name some of the ones that do this often) if the game crashes or sometimes after I quit the game my resolution gets set to 800x600 and I can no longer select 1920x1200 (it leaves the resolution as what ever it is currently).
If I try and play a game that I previously set the resolution to 1920x1200 it either crashes or gives me a D3D error.
The only way that I have found to fix this is to log out and back in or restart the computer.
I have updated my DX and ATI drivers/Catalyst Control Center to their latest releases but it still happens.
I am using Windows Vista Ultimate, my monitor is a Samsung SyncMaster T240, and my gfx card is an ATI Readon HD 4780 X2.
Is there anyway I can fix this problem permanently?