Installing and upgrading help

I recently completed the upgrade of our Moodle test instance from version
3.4.3-LAE14.0.2 to 3.4.6-LAE14.0.5 (this is the Liberal Arts Edition from
CLAMP).  We are using the CAS-SSO plugin to do single signon and this was
working perfectly under 3.4.3.  The upgrade process was fairly standard:
expanded the tar.gz file, move the old config.php over to the new directory,
pointed Apache's DocRoot to the new directory, and restarted the web service
(I also copied over the directories of the plugins/themes that are not part
of the standard LAE version).

When I accessed the new site for the first time, our CAS login page was displayed
and I successfully entered my University creds into the login page.  I was
then returned to the (/login/index.php) Moodle login page with the error
message "Invalid login, please try again".  If I again enter my credentials into
this form, I can gain admin access to the Moodle instance.  Completing
the automated upgrade process (I believe it was an "upgrading the database"
and then upgrading the existing plugins and themes), resulted in the same
behavior.
 
I've tried setting the debug level to "4:All relevant PHP error Messages" 
and looking at the CAS SSO settings within the Authentication section of
the plugins.  Neither produced any help.
 
I would welcome any suggestions on what may be wrong or how to troubleshoot   
this problem.
 
Thanks,
Mike