我该如何发布sql express数据库？

I have a simple app that uses an SQL Express 2005 database. When the user closes the app, I want to give the option to back up the database by making a copy in another directory. However, when I try to do it, I get "The process cannot access the file '...\Pricing.MDF' because it is being used by another process." I closed the connection, disposed the connection, set it to nothing, and GC.Collect(), but it makes no difference. My connection string is "Data Source=.\SQLEXPRESS2005;AttachDbFilename=|DataDirectory|\Pricing.mdf;Integrated Security=True; User Instance=True" and I just keep using the same connection throughout. I didn't see where I could detach the database to counter the attach in the connection string.I have a simple app that uses an SQL Express 20