Need help on setting stereo support for an opengl window

I’ve created an class wich encapsulates CWnd and I’ve created a function to engage the stereo support by setting the pixel format to support stereo. And if I am using this class into an application when I am creating first object of this class stereo support works; after I destroy my object and create a new one the stereo suport works (I mean I can write to the separatted buffers) but the glasses don’t start to cliping.
Please can anyone have an idea what is wrong?
I mention I have an 3DLabs Oxigene V1 video board and I am using Windows NT 4.0 sp 6 and Microsoft Visual C++ 6.0.