About Voodoo5 Video Card

I changed my video card recently, the new one is 3dfx Voodoo5. Now a problem appears. I find the function wglDeleteContext(hRC) does not work well. If I run our application in debug mood(Go F5) in Microsoft Visual Studio, it will go inside assembly code when this function(wglDeleteContext(hRC) ) is called. Although I can still go ahead, it is annoying. Is there anyone who know how to solve the problem? Please advise. Thanks a lot. My email is: yjzr@yahoo.com.