Case Summary: The link for the a customer to go directly to a case from the email link does not work for the authenicated user login approach.
Web+Center 4.0 Production
A link is provided in an email to the customer that allows them to quickly go directly to the support case rather than logging in and then selecting the case number. The link in the email is called DCF.asp (short for Direct Case Form). This assumes the users have a standard user login and password. If your customer+center is configured with authenticated user logins (refer to programmers guide on user authenication login methods), this email link will not work properly and that link should be changed to DCFAuth.asp instead of DCF.asp.
Perform a folder text search for DCF.asp in the techcenter and customercenter directories and replace it with DCFAuth.asp and make sure you have DCFAuth.asp module in your customercenter directory.