Frackal, are you using RivaTuner by any chance ?
If so, make sure that you enable the protection processes, during the installation you can select or un-select both types of protections, or after the installation, you can still very easily enable or disable one or both via the Power User options. The protection process will allow you to play any on-line games that use PunkBuster as an anti-cheat method.
If you're not using RivaTuner then I don't know what to say, it works just fine on my side.