RPC over HTTP Failing

[Rob]

I have a Win2003/Exchange 2003 (both standard edition) box behind our Netscreen firewall which I'd like to use for RPC over HTTP. I've followed the directions in the Exchange Server 2003 Deployment Guide but can't get Outlook to progress past the login screen. I keep giving it my credentials and it keeps prompting me for credentials.
a.. Server is single Exchange server, so there's no FE/BE issues.
b.. RPC over HTTP is installed
c.. OWA works properly.
d.. RPC directory security is set to Basic within IIS6
e.. Ports 80, 443, 593, 6001, 6002, and 6004 are forwarded to the Exchange server
f.. Since this is the only Exchange server, instead of enumerating the entire list of servers for the HKLM\Software\Microsoft\Rpc\RpcProxy key, I've set it to <machinename>:100-6000.
g.. Created a multi string value of NSPI interface protocol sequences in HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Parameters and set value to ncacn_http:6004.
On the WinXP SP1 Outlook client, I have installed the 331320 patch. I've set the profile:
a.. to encrypt data between server and client
b.. always prompt for username/password
c.. Kerberos/NTLM authentication
d.. connect to mailbox over http
e.. use the following URL for exchange proxy: <the http://fqdn of the server>
f.. connect using SSL only
g.. use http first on fast networks, then tcp/ip
h.. NTLM authentication when connecting to my proxy server
What am I missing?

Thanks,
Rob

 

[Lanwench [MVP - Exchange]]

Try posting this in microsoft.public.exchange.admin for best results.