[Zope] UserDB, IE5, @Home Problem

I am having trouble with userDB cookie authentication in IE 5 through the @Home network. Apparently @Home uses a proxy server for all of their traffic. When accessing the docLogin page for authentication the user receives a "Cannot Display This Page" error from IE 5. Turning off cookie-based authentication seems to solve the problem. This problem does not occur in Netscape under the same conditions and does not occur in IE 5 when used outside of the @Home proxy. Does anyone know of specific problems with IE 5 and proxy servers? Is there any solution outside of using standard authentication?