no suitable method found to override

using System;
using System.Data;
using System.Data.OleDb;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using ShoppingCartExample;
using System.Net.Mail;
using System.Text;
using System.IO;

public partial class CartControl : System.Web.UI.UserControl  
{
    OleDbConnection con = new OleDbConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ToString());

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Profile.SCart == null)
        {
            Profile.SCart = new ShoppingCartExample.Cart();
        }
        if (!Page.IsPostBack)
        {
            ReBindGrid();
        }
        if(Profile.SCart.Items == null)
        {
            TotalLabel.Visible = false;
            TotalLabelP.Visible = false;
        }

    }
    protected void grdCart_RowEditing(object sender, GridViewEditEventArgs e)
    {
        grdCart.EditIndex = e.NewEditIndex;
        ReBindGrid();
    }
    protected void grdCart_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        TextBox txtQuantity = (TextBox)grdCart.Rows[e.RowIndex].Cells[2].Controls[0];
        int Quantity = Convert.ToInt32(txtQuantity.Text);
        if (Quantity == 0)
        {
            Profile.SCart.Items.RemoveAt(e.RowIndex);
        }
        else
        {
            Profile.SCart.Items[e.RowIndex].Quantity = Quantity;
        }
        grdCart.EditIndex = -1;
        ReBindGrid();
    }
    protected void grdCart_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        grdCart.EditIndex = -1;
        ReBindGrid();
    }
    protected void grdCart_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        Profile.SCart.Items.RemoveAt(e.RowIndex);
        ReBindGrid();
    }
    private void ReBindGrid()
    {
        grdCart.DataSource = Profile.SCart.Items;
        DataBind();
        TotalLabel.Text = string.Format("Congrats Your Free shopping is of Rs : {0,19:}", Profile.SCart.Total);
        TotalLabelP.Text = string.Format("{0,19:}", Profile.SCart.TotalP);
       
    }
    
    
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        int tt = Convert.ToInt32(TotalLabelP.Text);
        int ttt = Convert.ToInt32(lbluserpoints.Text);

        if (tt >= ttt)
        {
            ScriptManager.RegisterStartupScript(this, GetType(), "showalert", "alert('You are exceeding the limits of your points , Kindly request to shop according to your points ..Thank You');", true);
        }
        else
        {
          int Remainpoints =  ttt - tt;
          con.Open();
          OleDbCommand cmdd = new OleDbCommand("UPDATE LOGIN SET CPoints =" + Remainpoints + " WHERE U_name = '" + txtusername.Text + "'", con);
            cmdd.ExecuteNonQuery();
            con.Close();
            //SendHTMLMail();
            
            ScriptManager.RegisterStartupScript(this, GetType(), "showalert", "alert('Thanks for connecting with us your Gift will be with you soon for more details please call 98*******');", true);
        
        }


    }
     //Method Which is used to Get HTML File and replace HTML File values with dynamic values and send mail 
    public void SendHTMLMail()
    {
        SmtpClient Smtp;

        MailMessage Msg = new MailMessage();
        MailAddress fromMail = new MailAddress("abc@yahoo.com");
        // Sender e-mail address.
        Msg.From = fromMail;
        // Recipient e-mail address.
        Msg.To.Add(new MailAddress("xyz@pune.com"));
        // Subject of e-mail
        Msg.Subject = "Request for Gifts";
        Msg.Body += "Please check below data <br /><br />";
        Msg.Body += GetGridviewData(grdCart);
        Msg.IsBodyHtml = true;

        Msg.Priority = MailPriority.High;

        Smtp = new SmtpClient("mail.pune.com");
        Smtp.Credentials = new System.Net.NetworkCredential("design@pune.com", "pwd123");
        Smtp.Port = 20;
        Smtp.Host = "mail.pune.com";
        Smtp.Send(Msg);



    }

    // This Method is used to render gridview control
    public string GetGridviewData(GridView gv)
    {
        StringBuilder strBuilder = new StringBuilder();
        StringWriter strWriter = new StringWriter(strBuilder);
        HtmlTextWriter htw = new HtmlTextWriter(strWriter);
        gv.RenderControl(htw);
        return strBuilder.ToString();
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        /* Verifies that the control is rendered */
    }
    
   
}