An attempt to attach an auto-named database for file

I'm getting the following error when running my application:

An attempt to attach an auto-named database for file C:\Users\Bryan\Documents\Visual Studio 2015\Projects\app\app.UI\App_Data\aspnetdb.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.

Here is my connection string:

 <connectionStrings>
    <add name="SoundyDB" connectionString="data source=BRYAN\SQLEXPRESS;initial catalog=MusicKarma;User id = BRYAN\bryan; password=; MultipleActiveResultSets=True;App=Soundy" providerName="System.Data.SqlClient" />
  </connectionStrings>

I want to use SQL-server and my Database MusicKarma.

When I debug my application and inspect the connectionString-variable, It has the following value:

connectionString = "data source=.\\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true"

I'm setting the connectionString variable this way:

public UserStore(string connectionString)
{
    if (string.IsNullOrWhiteSpace(connectionString))
    {
        throw new ArgumentException("Connectionstring");
    }
    this.connectionString = connectionString;
}

public UserStore()
{
    this.connectionString = ConfigurationManager.ConnectionStrings[0].ConnectionString;
}