[This advice is only pertinent to older Nvidia drivers]
If you are running under Windows XP with a Nvidia video card, the NVIDIA driver helper service overrides Adobe Gamma Loader from operating. If you meet those conditions the fix is to open "control panel"/"administrative tools"/"services". Then highlight the "NVIDIA driver helper service", right click and open properties. In the "Startup Type" drop down list change from Automatic to Disabled.
Every time you reinstall a new NVIDIA driver it enables the service again and you have to repeat the disable process.