The remote host is missing an update to freeswan announced via advisory DSA 201-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20201-1

Bindview discovered a problem in several IPSEC implementations that do not properly handle certain very short packets. IPSEC is a set of security extensions to IP which provide authentication and encryption. Free/SWan in Debain is affected by this and is said to cause a kernel panic. This problem has been fixed in version 1.96-1.4 for the current stable distribution (woody) and in version 1.99-1 for the unstable distribution (sid). The old stable distribution (potato) does not contain Free/SWan packages. We recommend that you upgrade your freeswan package.