ASP.NET: A network-related or instance-specific error occurred while establishing a connection to SQL Server

I have installed windows7 and SQL Server R2 and Visual Web developer 2008 express edition without SQL server 2008. Then I tried to open the asp.net configuration and tried to connect the default aspnet.mdf database using database explorer. It showed the following error message:

Provider: SQL network interfaces, error 26. error locating server/instances specified.

Solution:

I installed the visual web developer 2008 express edition with optional SQL server 2008 express edition then it solved the problem. 

Also:

1.     Download & Install IIS 7.0

2.     Using Turn windows features on or off - Install IIS feature