A few months ago I rebuilt my laptop and reinstalled Visual Studio 2008 and installed the SQL Server Express both x64 versions. When in a solution and trying to add a SQL Server database I would get the following error.
“Connections to SQL Server files (*.mdf) require SQL Server Express 2005 to function properly.”
I have been searching for a fix for this for the last few weeks and finally found this Microsoft Support hotfix.
This issue is only experiences on 64bit systems, 32bit systems are working correctly. Your system should also have Visual Studio 2008 SP1 or Visual Studio 2008 Express Edition with Service Pack 1 installed to apply this hotfix.