We have an SBS 2003 Standard R2 environment with ISA Server 2006 Standard on a separate Windows Server 2003 machine (Dual NICs). We cannot figure out how to publish OWA or any other SSL encrypted site hosted on the SBS machine. I have been through everything I can think of and all I get is the error in the question title. Currently the web listener has the 3rd party SSL certificate from Thawte and the web server has a self-signed certificate created using the CEICW. The ISA server is a Domain Member. What am I missing?