Database Mirroring: naming resolution issues during failover connectivity
Within a Database Mirroring session within an automatic failover situation it may fail with the error : "The server network address "%.*ls" can not be reached or does not exist. Check the network address name and reissue the command"
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Read the complete post at http://sqlserver-qa.net/blogs/ha/archive/2007/09/24/database-mirroring-naming-resolution-issues-during-failover-connectivity.aspx