This event is logged when the Microsoft Exchange System Attendant service comes online on an Exchange 2007 cluster node. See ME935676
for a workaround.
As per Microsoft: "Explanation: This event is indicating a failure to register SPN. This may prevent Outlook/OWA clients, running in a Kerberos-Only network, to get authenticated and logon to their mailbox. SPN "service principal name" gives a service running on a particular machine a global identity that allows it to authenticate via Kerberos. Exchange System Attendant is responsible for the SPN registrations of Exchange services.
User Action: SPNs are used by clients like Outlook to authenticate with the server. Verify that Outlook clients are able to log on and read mail, if not, try to restart MSExchangeSA. If that does not work, call Microsoft Product Support Services.
Users can also work around this problem by using a Windows utility called "setspn" that allows manual registration of SPNs on a machine. Exchange only registers "exchangeRFR" and "exchangeMDB" SPNs, which are used for Outlook authentication. By default, only domain administrators and local system can register SPNs. In some cases, Exchange administrators do not have any domain administrator rights; therefore they have to ask the domain administrator to run setspn".