I've talked about this before, but thought it was worth pointing people to this

Installing a Self-Signed Certificate as a Trusted Root CA in Windows Vista

[Today's post comes to us courtesy of Wayne McIntyre]

In order for RPC over Http to work you must have a Trusted CA Root Certificate installed and configured. In a situation where you are using a self-signed cert you will need to install the certificate into the Trusted Root Certification Authorities store.

1. Connect to your OWA site by going to https://host.domainname.com/exchange

FOR THE REST OF THE INSTRUCTIONS PLEASE FOLLOW THE LINK TO THE SOURCE BELOW

Source: The Official SBS Blog : Installing a Self-Signed Certificate as a Trusted Root CA in Windows Vista

ttfn

David