My code show error when insert data from C# to mssql

<pre><?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
    </configSections>
    <connectionStrings>
        <add name="Adipocytes_Diplomamunka.Properties.Settings.LipdatConnectionString"
            connectionString="Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Lipdat.mdf;Integrated Security=True"
            providerName="System.Data.SqlClient" />
    </connectionStrings>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
</configuration>

using System.Configuration;
using System.Data.SqlClient;
SqlConnection connection;
string connectionString;

        public Form1()
        {
            InitializeComponent();
            connectionString = ConfigurationManager.ConnectionStrings["Adipocytes_Diplomamunka.Properties.Settings.LipdatConnectionString"].ConnectionString;


        }

 private void button2_Click(object sender, EventArgs e)
        {

            SQLSU();
        }    

        private void SQLSU()
        {

            string query = "INSERT INTO Result VALUES(@ID, @Filename)";
            using (connection = new SqlConnection(connectionString))
            using (SqlCommand command = new SqlCommand(query, connection))
            {

                    connection.Open();

                    command.Parameters.AddWithValue("@ID", cnt);
                    command.Parameters.AddWithValue("@Filename", FileNa);
                    command.ExecuteScalar();

            }                     
        }