To resolve this error, try one of the following actions:
Make sure that you have configured the firewall on the server instance of SQL Server to open the SQL Server Browser port.
Make sure that the SQL Server Browser service is started on the server.
Check the spelling of the SQL Server instance name that is specified in the connection string.
Use the SQL Server Surface Area Configuration tool to enable SQL Server to accept remote connections. For more information about the SQL Server Surface Area Configuration Tool, see Surface Area Configuration for Services and Connections.