wgl and nvidia card

3

Please check if you’re actually running your OpenGL code on the NVIDIA implementation and not on the Intel one. (E.g. glGetString(GL_VENDOR))

Might be that P-Buffers are not supported on that implementation, which should have been found earlier when querying for the P-Buffer extension.
(P-Buffers should be considered legacy code and replaced with Framebuffer-Objects when possible.)

Related post: http://stackoverflow.com/questions/8220812/glgetstringgl-vendor-on-hybrid-graphics-machines