When I try to update the Red Hat Enterprise Linux 5.1 kernel, Yum fails with a syntax error. Why?

Issue

Red Hat Enterprise Linux 5.1 is installed in the system. The command "yum update kernel" is issued  to install the latest Red Hat Enterprise Linux 5.3 kernel. The Yum command fails with the following error message:

/sbin/mkinitrd: line 429: syntax error in conditional expression: unexpected token `('
/sbin/mkinitrd: line 429: syntax error near `^(d'
/sbin/mkinitrd: line 429: `        if [[ "$device" =~ ^(dm-|mapper/) ]]; then'
mkinitrd failed