KDC_ERR_S_PRINCIPAL_UNKNOWN

I got this error in the event log on a fresh Sharepoint Server 2010 February Cumulative Update installation:

A Kerberos Error Message was received:
 on logon session
 Client Time:
 Server Time: 17:6:26.0000 4/2/2011 Z
 Error Code: 0x7 KDC_ERR_S_PRINCIPAL_UNKNOWN
 Extended Error: 0xc0000035 KLIN(0)
 Client Realm:
 Client Name:
 Server Realm: DOMAIN.LOCAL
 Server Name: MSSQLSvc/sqlserver.domain.local:1433
 Target Name: MSSQLSvc/sqlserver.domain.local:1433@DOMAIN.LOCAL
 Error Text:
 File: 9
 Line: f09
 Error Data is in record data.

Solution:

The error is due to a dual SPN entry. I found this with

ldifde -f dump_spn.txt -d "dc=domain,dc=local" -p subtree -r "(servicePrincipalName=MSSQLSvc/sharepointsql*)" -l servicePrincipalName

I found that another account in addition to the SQL Server Service account had registered a SPN.

This was removed with adsiedit.msc: Navigate to the correct OU/User, and remove the servicePrinicpalName entry.