I saw this earlier and unlike most times I get an error, the answer was fairly obvious to me. I was calling a web service from a web application and they both lived on the same server and require SSL from a certificate. The problem was that my endpoint was set to use https://localhost/.... and the SSL certificate is actually for my domain name. I had to change the endpoint to include the full public domain name https://www.example.com/ which still resolves to the localhost but which then matches the SSL certificate name.