I was asked to try and find out why a web server could not communicate with the database. After checking all the usual network configurations I was beginning to despair. Together with the sys-admin we started firing off telnet connections, pings, etc, all worked but still SQL clients failed to connect. Finally by luck more than judgement the sys-admin attempted to connect to the database without the SQL instance name. Viola it worked. It seems that when you make a clustered virtual server it forms an alias from both the server names *and* the instance name, i.e. MyServer\MyInstance simply becomes MyClusterServer. We hadn’t had this problem on previous builds because we normally just have the default instance.