With SME8 going EOL this also has implications for upstream repos as CentOS has now archived the CentOS 5 repo tree.
See below for details for reconfiguring CentOS base and updates repositories for SME8 if needed.
db yum_repositories setprop base BaseURL '
http://vault.centos.org/5.11/os/$basearch/'
db yum_repositories setprop updates BaseURL '
http://vault.centos.org/5.11/updates/$basearch/'
db yum_repositories delprop base MirrorList
db yum_repositories delprop updates MirrorList
signal-event yum-modify
yum clean all