please fix this errors on my sample coding

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.Services;

using System.Web.Script.Serialization;

using System.Data.SqlClient;

using System.Data;

using System.Configuration;

using Newtonsoft.Json;

namespace ModelTest

{

public partial class PlayerEntry : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

}

[WebMethod]

public static string LoadData(int Flag)

{

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ToString());

string query = "select id, name, dob, gender, rating, status, Flag from tbl_Playersname where Flag="+Flag+" order by id desc";

SqlDataAdapter da = new SqlDataAdapter(query, con);

DataTable dt = new DataTable();

da.Fill(dt);

string jsonvalue = JsonConvert.SerializeObject(dt);

return jsonvalue;

}

[WebMethod]

public static string delete(int id)

{

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ToString());

string query = "update tbl_Playersname set Flag=0 where id="+id+"";

SqlDataAdapter da = new SqlDataAdapter(query, con);

DataTable dt = new DataTable();

da.Fill(dt);

string jsonvalue = "Successfully Deleted!!!";

return jsonvalue;

}

[WebMethod]

public static string adddata(string name, string dob, string gender, string rating, string status)

{

int rating1 = Convert.ToInt32(rating);

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ToString());

con.Open();

string query = "insert into tbl_Playersname values('" + name + "','" + dob + "','" + gender + "'," + rating1 + ",'" + status + "',"+1+")";

SqlCommand cmd = new SqlCommand(query, con);

cmd.ExecuteNonQuery();

con.Close();

return "successfully inserted!!!!";

}

}

}