Tengo un código para insertar valores en ASP.net usando vb. Tengo un problema con mi código que dice que el inicio de sesión falló, no se puede abrir la base de datos.

Dim struser, strpass, stremail As String
            struser = TextBox1.Text
            strpass = TextBox2.Text
            stremail = TextBox4.Text
            'declaring sql connection. 

            Dim thisConnection As New SqlConnection(ConfigurationManager.ConnectionStrings("DatabaseConnection").ConnectionString)

            'Create Command object
            Dim nonqueryCommand As SqlCommand = thisConnection.CreateCommand()


            Try
                ' Open Connection
                thisConnection.Open()

                Dim strcommand As String
                strcommand = "Insert into Account (Username,Password, Email) values ('" + struser + "','" + strpass + "','" + stremail + "')"

                Dim sqlcomm As New SqlCommand(strcommand, thisConnection)
                Dim o As String = sqlcomm.ExecuteNonQuery()


            Catch ex As SqlException
                ' Display error
                MsgBox(ex.ToString())
            Finally
                ' Close Connection
                MsgBox("Success")
                thisConnection.Close()


            End Try

Cadena de conexión

<add name="DatabaseConnection" connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=o2database.mdf;Integrated Security=SSPI" providerName="System.Data.SqlClient"/>