按照教程的步骤，我在App_Data文件夹中添加一个数据库文件，但是系统报如下错误信息：


经过才网络中搜索，发现先行者的记录：

Connections to SQL Server files (*.mdf) require SQL Server Express 2005 to function properly. Please verify the installation of the component ...
I've got this error message while trying to add a Database file into a c# website project :-s .
After a bit googling it appears that Visual studio 2005 is trying to connect to a SQLSERVEREXPRESS instance name, and yes this can be change easily, if like me, you have change this name during SQL server express 2005 installation. here we go:

In visual studio 2005, open the Tools menu
click on the "Options" item
Select the "Database Tools" node
Select the "Data Connections" child node

then you have a text box with the following label:
"SQL server Instance Name (blank for default):
"SQLSERVEREXPRESS"

for me it was just a matter of leaving it blank, and then adding a mdf file to the project is just working fine :-D
I've not found the solution anywhere else, I must be stupid... anyway, hope it helps someone.

于是到VS2008中去修改：
（注意，要将左下角的“显示所有设置”的复选框选上，否则看不到“数据连接”项）
将右边的SQLEXPRESS删除，确定。
 
我将SQLEXPRESS使用MSSQLSERVER替换。
但是，问题没有解决。
再搜索，发现如下方法：
You may open your Machine.Config file (the file is in %SystemRoot%\Microsoft.NET\Framework\ver. number\CONFIG ). Try to find the ConnectionString node, modify the setting and make it look like：

<add name="LocalSqlServer" connectionString="data source=.\MSSQLSERVER;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient" />

备注：红色字体原来为“.\SQLEXPRESS”

尝试下来，还是没有成功！始终报相同的错误信息。
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