Failure to add web part: error while establishing a connection to the server


When adding the smart search web part to my search results page, I get following error:
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)
My database servers have all the option checked to allow remote connections (both TCP/IP and named pipes.