I am going to assume you are looking for the definition and the root cause of these events:
SQL Server 2005 SP2 added new ring buffer entries RING_BUFFER_SECURITY_ERROR (sys.dm_os_ring_buffers) for various security errors. The reason the ring buffer entries were added was to provide the DBA with more details as to why a client is receiving a failed login or other such error. http://blogs.msdn.com/b/psssql/archive/2008/03/24/how-it-works-sql-server-2005-sp2-security-ring-buffer-ring-buffer-security-error.aspx. You state that you have no failed login entries in the event log nor in the errorlog. You can query this ring buffer directly:
SELECT CONVERT (varchar(30), GETDATE(), 121) as runtime,
dateadd (ms, (a.[Record Time] - sys.ms_ticks), GETDATE()) as [Notification_Time],
a.* , sys.ms_ticks AS [Current Time]
x.value('(//Record/Error/ErrorCode)', 'varchar(30)') AS [ErrorCode],
x.value('(//Record/Error/CallingAPIName)', 'varchar(255)') AS [CallingAPIName],
x.value('(//Record/Error/APIName)', 'varchar(255)') AS [APIName],
x.value('(//Record/Error/SPID)', 'int') AS [SPID],
x.value('(//Record/@id)', 'bigint') AS [Record Id],
x.value('(//Record/@type)', 'varchar(30)') AS [Type],
x.value('(//Record/@time)', 'bigint') AS [Record Time]
FROM (SELECT CAST (record as xml) FROM sys.dm_os_ring_buffers
WHERE ring_buffer_type = 'RING_BUFFER_SECURITY_ERROR') AS R(x)) a
CROSS JOIN sys.dm_os_sys_info sys
ORDER BY a.[Record Time] ASC
The notification time might shed some light on the root cause.
I think you will find that the date/time of the entries will line up with login failure entries in the errorlog similar to: "Login failed for user 'domain\user'. Reason: Token-based server access validation failed with an infrastructure error. Check for previous errors. [CLIENT: ] Error: 18456 Severity: 14 State: 11."
State 11 corresponds to “Valid login but server access failure” which indicates that the login is valid but is missing certain security privileges which would grant it access to the instance. Check if that login is directly mapped to one of the SQL Server logins by looking in the output of sys.server_principals. If the login is directly mapped to one of the available logins in the SQL instance, then check if the SID of the login matches the SID of the Windows Login. If someone dropped the login at the Windows/AD level, and added it back, it will get a new SID which won't match the SID SQL has stored in its system catalog and it will fail.