The one you are installing is meant for RHEL/CentOS 6.x.
Please try this instead:
rpm -Uvh http://mirror.symnds.com/distributio...5-4.noarch.rpm
Note: You may need to remove the existing EPEL repo if you run into issues.
Also, if possible without affecting production, you may want to upgrade your distribution to 5.10. There are many security vulnerabilities that are addressed through updates.