Generally we get following error when sql server is installed on another server
"An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections."
1. We can enable remote connections (on the machine that's running SQL Server) by running the SQL Server Surface Configuration Wizard (usually under Start->Programs->Microsoft SQL Server 2005->Configuration Tools->SQL Server Surface Area Configuration.
2. From there we click Surface Area Configuration for Services and Connections, choose the SQL Server Instance that we want to enable remote connections for and click the Local and remote connections under Remote Connections.
3. Now stop and start the service for that SQL Server Instance so that you're settings can take effect.