Upgrading to 12.04.5 and installing the Trusty kernel fixed the problem:
aptitude safe-upgrade
apt-get install --install-recommends linux-generic-lts-trusty
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Public bug reported:
iptables was working fine until I did an upgrade to a new kernel
version. Now it is impossible to load my firewall rules using iptables-
restore. The iptables-restore program croaks when trying to load the
rules.
While the error is reported on the line associated with the "