Setting up a new environment sometimes gets you into troubles. On my new laptop I didn't want to install SQL Server Express but only the developer edition of SQL Server 2005. Since I know there's a tool that ships with the .NET framework called aspnet_regsql, with which you can install the needed database for membership etc, I wanted to create such a database. Running the tool however I got this error message:
System.Web.HttpException: Unable to connect to SQL Server database. ---> System.Data.SqlClient.SqlException: 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: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
So ok, I set on remote connections for TCP/IP only but still got the same error. Strange, but true. So I searched for the error and found more information about it. Apparently the instance name of my database didn't get filled in automatically when using the wizard. Quickly inserting the correct instance name and all worked out like a charm.