Attempt to attach an auto-named database for .mdf file failed

I am currently building a Web Application Project in Visual Studio 2010 and, until recently, have not needed to use the scaffolded code for Memberships, Users and Roles etc that are stored in the ASPNETDB.mdf database file. I have been running the project on the Visual Studio Web Server, IIS Express (from Visual studio) and also IIS7.5 without a problem.

However, I now need to incorporate User accounts and when I use the scaffolded code to log in, I get a server error stating:

An attempt to attach an auto-named database for file C:UsersUserDocumentsCOMP6059PomumV2PomumV2App_Dataaspnetdb.mdf
failed. A database with the same name exists, or
specified file cannot be opened, or it is located on UNC share.

This error only occurs when I am using either the IIS Express or IIS7.5 web server. The Visual Studio Web Server works fine.

I have followed instructions from to no avail.

Below is my connection string for the database:

<add name="ApplicationServices"
     connectionString="data source=.SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true"
     providerName="System.Data.SqlClient" />

The error occurs on the following line of the AccountController.cs file (which is auto-generated)
...  if (Membership.ValidateUser(model.UserName, model.Password)) { ...

I did read somewhere that I might need to move the database into SQL Server Management Studio and then attach visual studio via that, but I was unable to log into the database.

I want this to be able to run on IIS7.5. Does anyone have any ideas on how to solve this issue?


Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

This is potentially an issue with the account you are running IIS under not having access to that file.

Assign full permissions to that folder for the Network Service account.

You can temporarily try ‘everyone’ and see if it resolves the issue, and work backwards from there.

Also ensure its not in use by the other web server (process explorer/sysinternals can help show you that)

Method 2

check that your folder is not read-only. Works for me

Method 3

It appears the OP has resolved the issue but I though it worthwhile tagging on my solution as it may help others in the future…..

I had a similar problem where the localDB went into apparent ‘Read-Only’ mode on the live server but worked fine on my local dev laptop.

After reading numerous post like this, and trying everything I could find, it still didn’t work.

By chance I went into IIS on the live server and noticed that there were 3 database connections identified. 2 were inherited -I dont know where from- and the third was locally declared(eg in the site web.config).

I deleted the 2 inherited connections and, voila! Now it works fine.

Method 4

Had this issue after migration from VS2013 to VS2015 Community, while tried to open project’s database .mdf file from Visual Studio 2013 folder. Then I copied project with database file to newly created Visual Studio 2015 folder and issue was solved.

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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