A common problem in using Response.Redirect is an error indicating that header modifications must be made before writing page content. The reason for this is that some HTML has been sent to the user's browser before the Response.Redirect call was made. The redirect directive is actually stored in the HTTP header sent along with the contents of the page, which is why you get an error complaining about header modifications.
If you're going to use Response.Redirect, you have to make sure that either you don't send any HTML, or you use Response.Buffer to buffer the output until you're done processing the page. If you do one of these solutions, it will eliminate the header errors.