yum - M2Crypto.SSL.SSLError: certificate verify failed

Yum is broken on one of my servers.

Today I re-registered 18 RHEL 5.x servers under the RHN Classic subscription model.
All 18 servers show as registered on the RH Customer Portal; However, this one won't allow any updates. On it, every use of the yum command, gets the error shown below.

I've compared everything I could to the other working servers and researched online forums, but cannot figure out why yum isn't working on this one server.

[root@saalvqad01 ~]# yum check-update
Loaded plugins: rhnplugin, security
Traceback (most recent call last):
File "/usr/bin/yum", line 29, in ?
yummain.user_main(sys.argv[1:], exit_code=True)
File "/usr/share/yum-cli/yummain.py", line 309, in user_main
errcode = main(args)
...
File "/usr/lib64/python2.4/site-packages/M2Crypto/SSL/Connection.py", line 167, in connect_ssl
return m2.ssl_connect(self.ssl, self._timeout)
M2Crypto.SSL.SSLError: certificate verify failed

$ cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.7 (Tikanga)

$ uname -a
Linux myhostname 2.6.18-274.el5 #1 SMP Fri Jul 8 17:36:59 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux

[snippets of /etc/sysconfig/rhn/up2date]
serverURL=https://xmlrpc.rhn.redhat.com/XMLRPC
disallowConfChanges=noReboot;sslCACert;useNoSSLForPackages;noSSLServerURL;serverURL;disallowConfChanges;
sslCACert=/usr/share/rhn/RHNS-CA-CERT

I've tried things like:
changing serverURL from https: to http: in /etc/sysconfig/rhn/up2date
yum clean all
rm -rf /var/cache/yum/*
yum makecache
re-registering, via rhn_register, after rm /etc/sysconfig/rhn/systemid. server registers, but yum remains broken.

I'm also aware of the old expired certificate issue, and dealt with that on 3 of the other servers, by copying a good certificate over.

Any advice/suggestions?