I was repeatedly getting an error when my red hat 8.0 box tried to contact the Red Hat Network (RHN). The error was related to the SSL certificate.
Initially, I put it down to the company firewall, but then later checked on the Red Hat site and found this (from http://rhn.redhat.com/help/latest-up2date.pxt)
"The certificate used by up2date and rhn_register to communicate with Red Hat Network reached its end of life on August 28th, 2003. Users attempting to connect to Red Hat Network will see SSL connection or certificate verification failures."
There was rpm udates for the up2date package along with instructions on how to install them. Note that I had to change the provided URLS to use HTTP rather than HTTPS to download them.