I am setting up a test mobile office server, and I
successfully send a registration message to a user. However
when trying to install on his handheld; the Setup hangs on
"Engine
Startup" , and then says "Cannot connect to server (503)"
Any ideas?

The server is configured with the following:

Proxy Server: obp21.obproxy.com
Proxy Port: 443
Proxy Protocol: https
Client Port: 5001

And the logs indicate that the server is communicating with
the proxy server corectly.