mdf file is work correctly under App_data folder but after attaching to sql server give following error

Question

mdf file is working correctly under App_data folder but after attaching it to sql server give following error when running asp.net page.

Cannot open user default database. Login failed. Login failed for user 'Domain\myUserName'.

[edit] More information; SQL data source and connection string.

<asp:SqlDataSource
        id="srcFiles"
        ConnectionString="Server=.\SQLExpress;Integrated Security=True;
            AttachDbFileName=|DataDirectory|FilesDB.mdf;User Instance=True"
        SelectCommand="SELECT Id,FileName FROM Files"
        InsertCommand="INSERT Files (FileName,FileBytes) VALUES (@FileName,@FileBytes)"
        Runat="server">
        <InsertParameters>
            <asp:ControlParameter Name="FileName" ControlID="upFile" PropertyName="FileName" />
            <asp:ControlParameter Name="FileBytes" ControlID="upFile" PropertyName="FileBytes" />
        </InsertParameters>
    </asp:SqlDataSource>

Answer 1

You can make sure that you are specify the correct sql username and password or you can give 'Domain\myUserName' access to your database. check out the connection strings below.

Connection string samples

Answer 2

I'm not sure how an MDF file is "working correctly" if it is just sitting in a folder and not attached to SQL Server. What do you mean by "working correctly"?

Anyway, what version of SQL Server? You can use sp_defaultdb to set the default database for that login to another database that you know is there, e.g.:

EXEC sp_defaultdb @loginame = 'Domain\myUserName', @defdb = 'tempdb';

TechNet: sp_defaultdb

If you are using SQL Server 2005 or 2008, you should use ALTER LOGIN instead, e.g.

ALTER LOGIN [Domain\MyUserName] SET DEFAULT_DATABASE = tempdb;

TechNet : ALTER LOGIN