An attempt to attach an auto-named database for file

问题： 

c:/inetpub/wwwroot/Demo/App_Data/aspnetdb.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.  

附加自动命名的数据库，但失败。已存在同名的数据库，或指定的文件无法打开或位于   UNC   共享目录中。”

解决方案：

Point 1:
Make sure U have Database.mdf file under app_data directory if you are using |DataDirectory| in the Connection String.

Point 2:
string connstring = @"Data Source=./SQLEXPRESS;AttachDbFilename=|DataDirectory|/Database.mdf;Integrated Security=True;User Instance=True";