I did a little research, here are some tips:
1. If you are running Win7, you will have to set up a "main monitor" in options. Right click on desktop, screen resolution. In the menu you can set up the first and second monitor, and do an automatic scan thingy. I would recommend running this. Although you can set up different resolutions for both monitors manually if first option doesn't help. Always chose "Recommended" resolution, it should be the one the monitor actually offers.
2. Run ATI Catalyst Control Center. Skip all "Auto-Setup"-Options if something like this pops up. Now you should see a menu for "desktop settings" with both monitors in a drop down menu. Check both monitors, if right resolution and color depth (32 Bit) is set, if not, correct the settings.
3. If tips above don't work, open up ATI Catalyst Control Center again. In top right corner you find "Options". Choose Options, Settings, Switch back to default settings.
4. Also: Look for updates for you graphic card or CCC.
I hope anything helps. I got the same setup (CCC with laptop and second screen), laptop hast 1920 x 1080 while second monitor has 1680 x 1050, I never had a problem with the setup or CCC.