Error message looked like this:
[~]# yum -y upgrade Loaded plugins: rhnplugin, security rpmdb: PANIC: fatal region error detected; run recovery error: db4 error(-30977) from dbenv->open: DB_RUNRECOVERY: Fatal error, run database recovery error: cannot open Packages index using db3 - (-30977) error: cannot open Packages database in /var/lib/rpm
Fix:
[ ~]# rm /var/lib/rpm/__db* [ ~]# rpm -rebuilddb [ ~]# yum clean all