su-to-root fails when root user locked?

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http://unix.stackexchange.com – How might I use script /usr/bin/su-to-root after I have intentionally locked the root account? Running Debian GNU/Linux 6.0.5 "squeeze" and noticed menu item "System > Administration > Synaptic Package Manager" has default command: su-to-root -X -c /usr/sbin/synaptic which fails even though I provide the correct root password. I have locked the root account (via command sudo passwd -l root) after granting my normal user sudo access via file /etc/sudoers. Via the su-to-root man page, I tried modifying the command to use a specific user: su-to-root -X -p "user" -c /usr/sbin/synaptic bu (HowTos)