Delete The Row I Written This Code Its Showing Some Error

ERROR:Index was out of range. Must be non-negative and less than the size of the collection.

protected void btnDelete_Click(object sender, EventArgs e)
    {
        //Loop through all the rows in gridview
        foreach (GridViewRow GridViewrow in GridView1.Rows)
        {
            //Finiding checkbox control in gridview for particular row
            CheckBox chkdelete = (CheckBox)GridViewrow.FindControl("chkdelete");
            //Condition to check checkbox selected or not
            if (chkdelete.Checked)
            {
                //Getting UserId of particular row using datakey value
             int Sno = Convert.ToInt32(GridView1.DataKeys[GridViewrow.RowIndex].Value.ToString());
                SqlDataSource1.DeleteParameters["Sno"].DefaultValue =Sno.ToString();
                SqlDataSource1.Delete();
            }
        }