ip_conntrack_pptp: error during exp_gre - what does this mean and how do I fix it?

["Greg Scott" <GregScott@xxxxxxxxxxxxxxxxxxx>]

Does anyone know what this error means?

Sep 12 00:50:16 xxxxx-fw kernel: ip_conntrack_pptp: error during exp_gre

These ocassionally show up in /var/log/messages on one of my firewalls.

I am using kernel 2.4.27 from kernel.org, iptables 1.2.11, and
patch-o-matic-20040621.

Thanks

- Greg Scott