The remote host is missing an update to psi announced via advisory DSA 1741-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201741-1

Jesus Olmos Gonzalez discovered that an integer overflow in the PSI Jabber client may lead to remote denial of service. The old stable distribution (etch) is not affected. For the stable distribution (lenny), this problem has been fixed in version 0.11-9. For the unstable distribution (sid), this problem has been fixed in version 0.12.1-1. We recommend that you upgrade your psi package.