Error handling implemented by IHttpModule doesn't work in IIS6, works in IIS5.1

I am implementing normal error handling using IHttpModule. Locally on my WinXP machine, it works like a charm. Once I upload the solution to our test server i.e. W2003 it doesn't work. After an error occurs, it displays directly on the asp.net error page. It doesn't handle my error module.

Any suggestion is most welcome .... X.