One or more prerequisites for protecting this data source is missing. Ensure that the following prerequisite software is ...

One or more prerequisites for protecting this data source is missing.
Ensure that the following prerequisite software is installed on %ServerName; and/or all nodes in the cluster.
Also ensure they are installed on the servers that are hosting a mirrored instance of SQL Server.

Windows Server 2003 SP1 with Knowledge Base article 940349 (http://go.microsoft.com/fwlink/?LinkId=99034)
        - OR -
Windows Server 2008 (http://go.microsoft.com/fwlink/?LinkId=128812)
SQL Server 2005 SP1 (http://go.microsoft.com/fwlink/?LinkId=77417)