Пишу веб-браузер, следующая ошибка:

Как исправить !? Вот код:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Browser
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
}
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
}
private void button1_Click_1(object sender, EventArgs e)
{
webBrowser1.Navigate("https://google.com");
}
private void button2_Click(object sender, EventArgs e)
{
}
private void button3_Click(object sender, EventArgs e)
{
webBrowser1.GoForward();
}
private void button4_Click(object sender, EventArgs e)
{
webBrowser1.GoBack();
}
}
}