I don't have any information on this type of error, and there are very few IPSec users on this forum.
I note that you also posted to misc@, and have not received any replies. I will guess that is because you have not provided any supporting information. Your report did not include a dmesg(8), and it did not include any of the possible IPSec configuration files you might have deployed. From memory, these could be:
- iked.conf
- ipsec.conf
- isakmpd.conf
- isakmpd.policy
You might consider reposting to misc@ with this missing information. Just redact any private information, such as Internet addresses and keys.