nah its to do with the the driver signing, the same thing happens with RivaTuner.
There is a command you can type in but it didnt seem to work, after that i got bored, but the other option i know of, in 7, is to press f8 on startup and on the boot menu under one of the menus/sub menus there is an option that says turn off windows driver signing.
Its prob the same with vista but i'm not sure as i never ran into this prob on vista.
Alternatively try powerstrip
http://downloads.guru3d.com/PowerStrip-3.75-download-169.html#download
it lets me go up to 997 mhz and has no mention of the driver signing issue on install