OWA F/E user access permission problem

HI..We have setup OWA on a fronend server in a DMZ(exchange 2003 with Server 2003), some users are unable to connect to the server remotely instead of the forms page opening they just get the windows logon dialog box and weather they entre the domain/username or just username they can not get on to the server.

Can any one help, I have setup logon locally permissions for all athenticated users on the owa server but this made no difference.

Brian