The cause of this KDC event is the client computer is sending a service ticket request with an etype that is not supported by the Windows Server 2003 domain controller (the etype is supported for the Windows 2008 domain controller). This event is informing the client as to what etype it supports. The Windows Vista or later client computers are falling back to the supported types.
For more information see the following articles:
Event ID 26 - KDC Encryption Type Configuration (http://technet.microsoft.com/en-us/library/cc734055(WS.10).aspx)
Kerberos Enhancements (http://technet.microsoft.com/en-us/library/cc749438.aspx)
KB 978055 (http://support.microsoft.com/kb/978055)
This article was derived from the DS forum post, EventID 26 & 27 : KDC: suitable keys (http://social.technet.microsoft.com/Forums/en-US/winserverDS/thread/29f55875-f3ee-476c-9d74-94f1b74edb31)
Fernando Lugão Veltem edited Revision 5. Comment: added table