[CentOS] yum-updatesd no longer working

I recently enabled yum-updatesd on two identical servers and configured
it to notify me of updates via e-mail.

This worked fine to start with and it notified me on both machines when
the kernel-2.6.18-128.1.10.el5.x86_64.rpm update was released last week.

However, today I realised that yum-updatesd was not running and thought
it was due to rebooting after the kernel update and that I'd forgotten
to set it to start at boot.

But this was not the case, it is set to start, however running
'/sbin/service yum-updatesd start' yields:

yum-updatesd dead but subsys locked

I have tried removing /var/lock/subsys/yum-updatesd, but when I restart
the service it says [OK] and yum-updatesd doesn't run, but the lock file
is re-created.

yum-updatesd --debug does not help either.

Any help or idea's greatly appreciated.

Thanks