Database Connection error - sql

Question

I have win application and i get this error when i want to connect the database to my app
error:
An attempt to attach an auto-named database for file C:\Users\Aren\Desktop\DB\REGISTRATION.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.
public class DALBase
{
protected SqlConnection con = new SqlConnection(#"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\\Users\\Aren\\Desktop\\DB\\REGISTRATION.mdf;integrated Security=true ; User Instance=True");
protected SqlCommand com = new SqlCommand();
protected SqlDataAdapter da = new SqlDataAdapter();
protected DataSet ds = new DataSet();
}
public DataSet GetStudent(string filter)
{
DataSet dset = new DataSet();
using (SqlCommand cmd = new SqlCommand())
{
string cmdstring = string.Format("Select * from {0}"
, Common.Data.Student.Table_Name);
if (!string.IsNullOrEmpty(filter)) cmdstring += " where " + filter;
cmd.CommandText = cmdstring;
cmd.Connection = this.con;
cmd.Connection.Open();
cmd.CommandText = cmdstring;
cmd.Connection = this.con;
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dset, Common.Data.Student.Table_Name);
return dset;
}
}
NOTE: ALSO i got 3 project in my solution the DALBASE and GETSTUDENT methods are in one project and i call them from other project to get the data for me.

Answer 1

I believe i have encountered this problem in the past. in my situation I loaded an application in visual Studio which when run would load a database and attach to SQL Server. Somehow when I closed the application it didn't deattach the database from SQL SERVER and next time I ran the app it complained with a similar if not the same message.
If you have SSMS installed open up to the .\SQLEXPRESS instance and see if you have a Registration*.mdf file attached. Or if you don't have SSMS open up your command line and type...
sqlcmd -S .\SQLEXPRESS -Q "select name from sys.databases"
This will show you all your databases attached/online on that instance.
Hope this helps.