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Editorial Team
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Asked: 2026-05-30T14:02:21+00:00

I’m having some problems consistently connecting to my database via a connection string from

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I’m having some problems consistently connecting to my database via a connection string from Visual Studio 2010, and in SSMS. The connection string worked reliably for weeks… when I worked with the database in SSMS, the connection string stopped working. “Login failed” error. In my efforts to apply the solutions given to other people with extensive searching, I was able to connect, once, by detaching the database in SSMS. I restarted SSMS and the database appeared in object explorer, but the full path was given as the name. Now I can’t work with the database, as you can see below in object explorer:

enter image description here

I’m not sure if it needs to be attached, as I’ve tried and that generates an error as well. So I’d really appreciate a little guidance on using an SQL Server 2008 R2 Express database from .NET, as well as SSMS. I’m the only user, it’s a local instance, and simplicity and reliability would trump any custom security settings. If it’s of interest, here’s the connection string I’ve been using:

connectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=""C:\Program Files\Microsoft SQL Server\MSSQL10_50.SQLEXPRESS\MSSQL\DATA\Market.mdf"";Integrated Security=True;Connect Timeout=600;User Instance=False";

There is an abundance of forum posts/ solutions as well as articles on this exact issue, but I haven’t been able to get anything I’ve found thus far to work. Punting… can anyone get me on track?

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1 Answer

  1. Editorial Team

    Detach the database (right-click, detach).

    Open a New Query Window.

    Attach the database.

    CREATE DATABASE Market ON 
(FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL10_50.SQLEXPRESS\MSSQL\DATA\Market.mdf')
FOR ATTACH;

    Now you can connect to the database by name. Your connection string should be:

    connectionString = @"Data Source=.\SQLEXPRESS;Initial Catalog=Market;Integrated Security=True;";

    You should rarely, if ever, want to use the AttachDbFilename and User Instance features on purpose. These are the cause for all of the Google hits you came up with.

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