Connection to a named instance of SQL server 2005/2008 should be made using the format
‘VirtualServer\Instancename’. if the IP address of a machine running a named SQL server instance
(ONE)is 220.127.116.11, you can connect to the named instance using 18.104.22.168\ONE for the servername.
To avoid a client app from using the above convention for a servername, a client alias can be created using the client network utility. Client network utility can be initiated by
Start->Programs ->Microsoft SQL Server->Client Network Utility
and you can create a Named Pipes or TCP/IP alias for your server and try connecting again.