SetPixelFormat and nvidia drivers

I have developed software on a GeForce3 with drivers 30.82 and all works well. I have upgraded to a GeForce4 and ran into problems.
The wglMakeCurrent call takes way too long (~20ms). All other calls, drawing and glReadPixels, take the same amount of time as they used to. What happened?

As a fix, I tried to upgrade to drivers 40.72 and 43.45 and SetPixelFormat fails even though the PixelFormatDescriptor as filled out by DescribePixelFormat after it describes the format chosen by choosePixelFormat is exactly the same. Don’t the new drivers support at least as many formats as they used to? Why would ChoosePixelFormat return a format type that would then fail in SetPixelFormat? Any help would be greatly appreciated.