Unable to get updates from RHN

For reasons unknown, Since 12/18, we've not been able to pull any
updates from RHN. I can login to RHN via web and see that updates are
available for our 3 registered servers (all are RHEL 5.3), yet when I
run yum check-update or run package updater (pup), it shows no updates
available ... How do we go about debugging this or getting it fixed ?
I've tried re-registering via rhn_register, but that seems to create
duplicate entries on RHN for the same machine !!

Regards,

Paul Goslin
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