The following pages were recently modified. Source: Knowledge Base Product: Microsoft SQL Server 2005 Standard Edition Notification Contents: New and All Modifications FIX: Event ID: 21421 occurs when you use the Microsoft Operations Manager 2005 agent to monitor a clustered instance of SQL Server 2005 in a clustered environment http://support.microsoft.com/kb/938911/en-US...(
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Read the complete post at http://sqlserver-qa.net/blogs/kba/archive/2007/09/19/2124.aspx