Page controls do not exist in the current context
<p>In my design part I have added all labels and Dropdown lists but in register.aspx.cs, it shows these controls do not exist in the current context..</p>

<pre><code>    using System;    
    using System.Collections;    
    using System.Configuration;    
    using System.Data;    
    using System.Linq;    
    using System.Web;    
    using System.Web.Security;    
    using System.Web.UI;    
    using System.Web.UI.HtmlControls;    
    using System.Web.UI.WebControls;    
    using System.Web.UI.WebControls.WebParts;     
    using System.Xml.Linq;    
    using System.Data.SqlClient;  
    using System.IO;


    public partial class register : System.Web.UI.Page    
    {    
    SqlConnection con = new SqlConnection("server = .\\SQLEXPRESS;AttachDbFileName    =|DataDirectory|\\Database123.mdf;trusted_connection = true;USER Instance =yes");    
    protected void Page_Load(object sender, EventArgs e)
    {

    }



    protected void Button2_Click(object sender, EventArgs e)
    {


        try
        {

            if (CheckBox1.Checked == true)
            {
                String f;
                f = Path.GetFileName(FileUpload1.FileName);
                con.Open();
                if (f != "")
                {

                    FileUpload1.SaveAs(Server.MapPath("~") + "/images/" + f);
                    Label2.Text = "~" + "/images/" + f;

                    SqlCommand cmd1 = new SqlCommand("insert into register values('" + TextBox1.Text + "','" + TextBox8.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + RadioButtonList1.SelectedValue + "','" + TextBox4.Text + "','" + DropDownList3.SelectedItem + "','" + DropDownList2.SelectedItem + "','" + TextBox7.Text + "','" + TextBox10.Text + "','" + RadioButtonList2.SelectedValue + "','" + TextBox12.Text + "','" + Label2.Text + "','" + DropDownList1.Text + "','" + TextBox14.Text + "')", con);
                    cmd1.ExecuteNonQuery();
                    TextBox1.Text = " ";
                    TextBox8.Text = " ";
                    TextBox2.Text = " ";
                    TextBox3.Text = " ";
                    TextBox4.Text = " ";
                    // TextBox15.Text = " ";
                    // TextBox16.Text = " ";
                    TextBox7.Text = " ";
                    TextBox10.Text = " ";
                    TextBox12.Text = " ";
                    TextBox14.Text = " ";

                    Label1.Visible = true;
                    Label1.Text = "submitted successfully";
                }

                else
                {

                    SqlCommand cmd1 = new SqlCommand("insert into register(user_id,password,fname,lname,user_type,address,city,state,pin,contact_no,gender,email,seq_que,seq_ans) values('" + TextBox1.Text + "','" + TextBox8.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + RadioButtonList1.SelectedValue + "','" + TextBox4.Text + "','" + DropDownList3.SelectedItem + "','" + DropDownList2.SelectedItem + "','" + TextBox7.Text + "','" + TextBox10.Text + "','" + RadioButtonList2.SelectedValue + "','" + TextBox12.Text + "','" + DropDownList1.Text + "','" + TextBox14.Text + "')", con);
                    cmd1.ExecuteNonQuery();
                    TextBox1.Text = " ";
                    TextBox8.Text = " ";
                    TextBox2.Text = " ";
                    TextBox3.Text = " ";
                    TextBox4.Text = " ";
                    // TextBox15.Text = " ";
                    //TextBox16.Text = " ";
                    TextBox7.Text = " ";
                    TextBox10.Text = " ";
                    TextBox12.Text = " ";
                    TextBox14.Text = " ";

                    Label1.Visible = true;
                    Label1.Text = "submitted successfully";
                }
                con.Close();

            }
            else
            {
                Label1.Visible = true;
                Label1.Text = " terms &amp; condition must checked";
            }
        }
        catch (Exception e1)
        {
            Response.Write("&lt;script language='javascript'&gt;alert(\"Invalid Data Entry\")&lt;/script&gt;");
        }

        }
    protected void  DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {

    if (DropDownList2.SelectedIndex == 1)
        {
            DropDownList3.Items.Clear();
            DropDownList3.Items.Add("jaipur");
            DropDownList3.Items.Add("udaipur");
            DropDownList3.Items.Add("ajmer");
            DropDownList3.Items.Add("bharatpur");
            DropDownList3.Items.Add("tonk");
        }
        else if (DropDownList2.SelectedIndex == 2)
        {
            DropDownList3.Items.Clear();
            DropDownList3.Items.Add("amravati");
            DropDownList3.Items.Add("mumbai");

        }
    }

    protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
    {

    }
    }
</code></pre>
