Did a search and found numerous references to the missing sysstat plugin. Bear with me, I'm not a RedHat guru by any stretch.
RHEL 5 32-bit
Get the standard "sysstat is missing" message. Tried to install:
[root@zimbra ~]# yum install sysstat
Loaded plugins: rhnplugin
Error: failed to retrieve repodata/primary.xml.gz from rhel-i386-server-5
error was [Errno 14] HTTP Error 500: Internal Server Error
Am I missing some other pre-sysstat dependency?