VERIFIED! Since web ui does not allow user to add a new system, the validation was performed via CLI, making sure to set the number of sockets to zero:

# echo '{"cpu.cpu_socket(s)":"0"}' > /etc/rhsm/facts/sockets.facts
# subscription-manager facts --list | grep cpu.cpu_socket
cpu.cpu_socket(s): 0
lscpu.cpu_socket(s): 1
# subscription-manager register --username admin --password admin --org 'SAM QE' --env 'QE Env'
Validation failed: Sockets must be greater than 0

* candlepin-0.7.23-1.el6_3.noarch
* candlepin-tomcat6-0.7.23-1.el6_3.noarch
* elasticsearch-0.19.9-5.el6_3.noarch
* katello-candlepin-cert-key-pair-1.0-1.noarch
* katello-certs-tools-1.2.1-1h.el6_3.noarch
* katello-cli-1.2.1-11h.el6_3.noarch
* katello-cli-common-1.2.1-11h.el6_3.noarch
* katello-common-1.2.1-10h.el6_3.noarch
* katello-configure-1.2.3-1h.el6_3.noarch
* katello-glue-candlepin-1.2.1-10h.el6_3.noarch
* katello-headpin-1.2.1-10h.el6_3.noarch
* katello-headpin-all-1.2.1-10h.el6_3.noarch
* katello-selinux-1.2.1-1h.el6_3.noarch
* thumbslug-0.0.28-1.el6_3.noarch
* thumbslug-selinux-0.0.28-1.el6_3.noarch

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-0544.html