Cannot add a .mdf file to VS 2010 using SQL Server 2008 R2 Developer Edition

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SQL-Server

Visual-Studio

I have installed SQL Server 2008 R2 with the instance name of SQLSERVERR2. When I am using the instance I cannot add a .mdf file to the ASP.Net App_Data folder. The error is "A network related error or instance related error occurred while establishing a connection to SQL Server". I have tried configuring the instances' TCP/IP configuration but the result is the same. But when I am using the default SQL Server 2008 Express that installed with the VS 2010, it can be used to add the .mdf file to the App_Data folder successfully!

I have to use the .mdf file with the SQL Server 2008 R2 Developer. Then what should I do ?

I have tried this using VS 2010 Professional & VS 2010 Ultimate. But gave the same result.

I don't know what to do. Please someone can help me.

Thank you

Chiranthaka.