error: 28 - Server doesn't support requested protocol

After trying to setup SQL Server 2005 Express, I kept getting the following error when I tried to connect from a web application:

"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)"

Network protocols are disabled in SQL Server 2005 Express by default so we need to enable TCP/IP:

Launch the SQL Server Configuration Manager

Expand the "SQL Server 2005 Network Configuration" node

Left click the "Protocols for SQLEXPRESS" node to view the supported protocols

Right click the "TCP/IP" protocol and select "Enable"