I stumbled on this thread while trying to figure out why RPC-HTTP was not working on one of the networks I administer. (Note: I inherited this network, and all it's problems.) From reading people's posts, I was able to solve half the problem and I figured out the rest so I figured I'd share what worked for me...
1 ISA 2000 Firewall (on w2k), 1 Stand-Alone Exchange 2003 server with RPC-HTTP "enabled" (on w2003) also acting as the only dc and gc. Outlook 2003 clients all using RPC-HTTP over the LAN but unable to use RPC-HTTP over WAN due to "crappy Microsoft software" (or so claimed the outgoing IT guy)!
First thing I did was verify that RPC-HTTP was installed and enabled on the exchange server. Then I did some testing and discovered that the LAN clients were actually connecting via unencapsulated TCP/IP*! The previous IT guy had set Outlook to use RPC-HTTP, but did not realize that in the absense of a working HTTP connection, Outlook falls back to normal RPC. Note: If your exchange connection manager claims "TCP/IP" you're using unencapsulated RPC, if it claims HTTPS then RPC-HTTP is working.
After some sluthing and reading of this, and other forums, I determined that the ValidPorts registry key for the RPC proxy was incorrect. I cheated, and copied the key value from a SBS server that I also administer, and then changed the names as appropriate. This is the key that worked for me for a stand-alone Exchange RPC-HTTP implementation:
Once I changed that, then LAN clients could connect via RCP-HTTP.
ThenI turned my attention to WAN clients. That proved to be very simple. I trouble-shot like crazy, and could not figure why it was not connecting. OWA worked, and I could access the RPC directory via the Internet. I was so frustraited, it was not even funny. Turns out I had overlooked something incredibly simple. When the previous guy had installed URLScan on the ISA server, he claimed that he had installed the OWA configuration and then modified it to allow RPC-HTTP. I had briefly scanned the ini and it looked correct. It was my bad, and I should ahve read it more closely. He had made all the appropriate changes, except one. He forgot to add RPC_OUT_DATA to the Allow Verbs. He had added RPC_IN_DATA, but apparently did not think that the RPC_OUT_DATA was important.
So yeah, what fixed it for me was getting the ValidPorts key fixed, and making sure URLScan.ini was correct.
As a thought for those of you able to connect VIA LAN but not WAN, make sure that your URLScan.ini files are correct. And not just on the firewall either. Did any of you install it on your RPC-HTTP server? There is an IIS version as well as an ISA version. If so, chack those as well.
Hope this helps someone!
* Tom, I wanted to give you a heads-up... In your great (saved my bacon a couple of times) Exchange 2003/ISA 2000 deployment kit on the page for "Connection to Exchange via RPC over HTTP through ISA Server 2000" (http://www.isaserver.org/img/upl/exchangekit/2003rpchttp/2003rpchttp.htm) you write "This is an interesting setting, as its unclear what a ôLANö protocol is in contrast to an ôHTTPö protocol. I assume it means to use unencapsulated RPC messages, but I canÆt say that for sure." when talking about configuring the client, the production version of Outlook 2003 is less confusing. Its choice is to connect via HTTP or TCP/IP, which means HTTP encapsulated RPC or straight RPC over TCP/IP. Just as an FYI, don't know if that helps at all.