An error has occurred while establishing a connection to the server

Problem:

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. (provider: SQL Network Interfaces, error: 28 - Server doesn't support requested protocol) (Microsoft SQL Server, Error: -1)

Resolution:

Check the below setting at Server Level
1. Check the firewall for any blocking (i.e TCP/IP Port:1433)
2. Check the SQL Server Instance Name, there may be chances of the spelling mistakes
3. May be remote connection is disable. Use the SAC (SQL Server Surface area configuration tool for remote connection)
4. Check the status of SQL Browser Service, it should be running to allow remote connectivity