You don't have the proper Certification Authorities (CAs) installed on the
machine that you are using to connect to the secure server.
I show a couple CAs in the certificate path that should be imported. If
you think they are there, try importing them one at a time again starting
from the top level CA, down the levels to the last one.
I have some instructions that will help retrieve the CAs and import them in
the SSL documentation at http://docs.bvstools.com