SQL Network Interfaces, error: 26 in DNN

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: 26 - Error Locating Server/Instance Specified)

You may experience above errors when using some old modules. It is because the old module is developped using old method to retrieve the connectionString.

To fix the error:

Open web.config, make sure the connectionString in ConfigSections is the same as the SiteSQLServer in appSettings.