Error connecting to ms sql server via c #

There is an authorization form when you enter a value and click on the input button, an error appears. PS The program code is described below.

using System; using System.Collections.Generic; using System.ComponentModel; using System.Configuration; using System.Data; using System.Data.SqlClient; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace Voyage { public partial class fAuthorization : Form { string connectionString = ConfigurationManager.ConnectionStrings["SqlCon"].ConnectionString; SqlConnection connection; public fAuthorization() { InitializeComponent(); topPanel.BackColor = Color.FromArgb(0, 71, 160); headerLabel.ForeColor = Color.White; lLogAndPassword.ForeColor = Color.FromArgb(0, 71, 160); signInBtn.BackColor = Color.FromArgb(0, 71, 160); lLog.ForeColor= Color.FromArgb(0, 71, 160); lPassword.ForeColor = Color.FromArgb(0, 71, 160); seePassword.ForeColor= Color.FromArgb(0, 71, 160); lCopyright.ForeColor = Color.FromArgb(0, 71, 160); shutdownBtn.BackColor= Color.FromArgb(0, 71, 160); } private void seePassword_CheckedChanged(object sender, EventArgs e) { if (seePassword.Checked) tbPassword.UseSystemPasswordChar = false; else tbPassword.UseSystemPasswordChar = true; } private void shutdownBtn_Click(object sender, EventArgs e) { this.Dispose(); } private void signInBtn_Click(object sender, EventArgs e) { SqlDataReader reader; string role = ""; string username = ""; try { using(connection = new SqlConnection(connectionString)) { string command = String.Format("Select sLog, sRole From tUser Where " + "(sLog='{0}' Collate SQL_Latin1_General_CP1251_CS_AS) and " + "(sPassword='{1}' Collate SQL_Latin1_General_CP1251_CS_AS)", tbLog.Text, tbPassword.Text); SqlCommand Select = new SqlCommand(command, connection); reader = Select.ExecuteReader(); if (reader.HasRows) { while (reader.Read()) { username = reader[0].ToString().Trim(); role = reader[1].ToString(); } tbLog.Text = ""; tbPassword.Text = ""; MessageBox.Show(username, role); /* MainMenu mm = new MainMenu(role, username); mm.Owner = this; mm.Show(); this.Hide();*/ } else { MessageBox.Show("Неверные логин или пароль", "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Error); } } } catch (Exception ex) { MessageBox.Show(ex.ToString()); } } } }