OWA via SBS 2003 STD plus ISA 2004

I just installed SBS 2003 and have EXCHANGE and ISA 2004 running on this machine. This machine’s IIS is serving up OWA to internal clients just fine, but not to external clients. IIS has grabbed port 443 and won’t let ISA publish OWA on 443. I adjusted the ISA policy to listen on 440 and forward to 443 (listener and binding tabs) and that got external users to the OWA logon screen, but after they input their logon credentials, the next page returns a screen with two panels – having page not found message

By the SBS log entries, it appears that the users are logged in and then immeadiately logged out

does anyone have any ideas?
is it an issue with R&R, ISA, IIS, folder permissions, security, etc?