Can't access Local SQL database manually by connection string in VB.NET using Visual Studio

I have a project set up with 3 separate tables. I used the built-in designer from Visual Studio.

The tables contain

1. Students
2. Courses
3. Tests in each course

All the tables share a studentnumber.

I have no problem getting and accessing the data true different tableadapters and corresponding bindingsources automatically generated by Visual Studio when I "drag and drop" them on the forms. I also am able to use the query builder to get the data I need from each table.

My problem occurs when I try to access the database manually via connection string.

I get this error:

Cannot attach file local path\HovedDatabase.mdf as database Outcomes because the file is already in use for database local path\HovedDatabase.mdf

This is the code I have:

Private Sub FormPrøver3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'TODO:   This line of code loads data into the 'StudentDataSet.StudentTabell' table. You can move, or remove it, as needed.
    Me.StudentTabellTableAdapter.Fill(Me.StudentDataSet.StudentTabell)
    Me.StudentTabellTableAdapter.Connection.Close()

    Get_Data_Manualy_Fag()

End Sub

Private Sub Get_Data_Manualy_Fag()
    Try
        'Create variabals for inputcontainer
         Dim Studnr As String = Me.StudentnrLabel1.Text

        'Create a connection to the DataBase
        Dim myConn As SqlConnection
        myConn = New SqlConnection("Initial Catalog=OutComes;Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\HovedDatabase.mdf;Integrated Security=True")

        'Create a Command object.
        Dim myCmd As SqlCommand
        myCmd = myConn.CreateCommand
        myCmd.CommandText = "SELECT Fag FROM Fag3Tabell WHERE Fag = @Studnr"
        myCmd.Parameters.AddWithValue("@Studnr", Studnr)

        'Open the connection.
        myConn.Open()

        'Process the answer
        Dim myreader As SqlDataReader
        myreader = myCmd.ExecuteReader

        'Traverse the DataSet and Display :
        Dim i As Integer = 0
        Do While myreader.Read()
            Me.ComboBox1.Items.Add(myreader.GetString(i))
            i = i + 1
        Loop

        'Close the connection
        myConn.Close()

        'Handle errors
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try

I set up a similar project with a similar LocalSQL database. I have done nothing in Visual Studio other than creating the database with the same tables.

Here I have no problem connecting to the database via manual connection string.

My question is: why can't I access the local DB with a connection string in the first project?