protected void btn_login_Click(object sender, EventArgs e)
    {
        string error_msg;
        int?   ID = Users_Query.Get_User_ID(out error_msg, tb_user.Text, tb_pass.Text);

        if (ID != null)
        {
            Session["User_id"] = ID;
            Server.Transfer("MonsterList.aspx", true);
        }
        else
        {
            error_lbl.Text = error_msg;
        }
    }
    protected void btn_register_Click(object sender, EventArgs e)
    {
        string error_msg;
        int?   ID = Users_Query.Register_User(out error_msg, tb_user.Text, tb_pass.Text);

        if (error_msg.Equals("Invalid Credentials"))
        {
            error_lbl.Text = "Either Password or User Name is already in use";
        }
        else
        {
            error_lbl.Text = "Registration successful";
            Creatures_Query.Create_Default_Creatures(Users_Query.Get_User_ID(out error_msg, tb_user.Text, tb_pass.Text));
        }
    }