To unlock the RPM database, in a console as root run:
# rm -f "/var/lib/urpmi/.LOCK"
# rm -f "/var/lib/urpmi/.RPMLOCK"
Be sure that the auto check program is not running. If it is, there is a little icon in the tray, near the clock. (KDE) If it is running, close it, and that will unlock the database.
If a package is holding up updates, then unselect the package, run updates, and try again. I would also suggest updating your software sources before running again.