OWA Login Problems

This the scenario

1. Exchange Server 2003 … OWA enable with form-based authentification.
2. Isa Server 2004 … Publishing Mail Server Rule working fine. (from inside and outside the network)

Problems

1. Cannot login using the owa.mailserver.com/exchange but works great inside the network owa.mailserver.local/exchange

Tips

No errors receive when the user logins … just go back to the same login form.

any help please ?