The remote host is running an inherently insecure protocol or application.
The remote host is running Kerberos 4. It has been demonstrated that the Kerberos 4 protocol has inherent design flaws that make it insecure to use.
Upgrade to Kerberos 5. If you run Kerberos 5 with Kerberos 4 backward compatibility, make sure you upgrade to version 1.3.