Can't create roles and membership

 I used to have the membership roles working, but recently when I create a new web site and click on the Security Tab in the Website Admin Tool, I get ...

A
network-related or instance-specific error occurred while establishing
a connection to SQL Server. The server was not found or was not
accessible. Verify that the instance name is correct and that SQL
Server is configured to allow remote connections. (provider: SQL
Network Interfaces, error: 26 - Error Locating Server/Instance
Specified)
 I looked at the web site Properties Page and it is set to use the default web server.  How do I convince the program to set up the roles and membership databse?

I have updated VWD Express 2008 and  SQL Server 2005 Express and other stuff too (can't remember what as I have been ...