急！急！急！請問win32api參數亂碼如何解決！

　　我想作一個QQ自動登錄，使用的QQ是2009.如今先模擬打開QQ，而後經過api調用回調函數。回調函數爲一個委託方法，可是在方法中整個參數亂碼，請問如何解決？

　　具體流程爲，啓動QQ，獲取當前啓動QQ的句柄，經過EnumChildWindows方法回調方法，可是在EnumWindowsProc中，account和pwd亂碼。請問如何解決？

        public delegate bool CallBack(IntPtr hwnd, int lParam, string account, string pwd );


        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern IntPtr EnumChildWindows(IntPtr hWndParent, CallBack lpEnumFunc, int lParam);

       /// <summary>
        /// QQ登陸
        /// </summary>
        public static void LoginIn(string account = "123456", string pwd = "123456")
        {
            //啓動QQ程序
            StartCmd();

            IntPtr h;
            string strName = "QQ2009";
            h = FindWindow(null, strName);
            if (h.ToInt32() != 0)
            {
                MoveWindow(h, 0, 0, 350, 300, true);
                CallBack myCallBack = new CallBack(EnumWindowsProc);
                EnumChildWindows(h, myCallBack, 0);
            }
        }

        /// <summary>
        ///將鼠標移動到登錄按鈕
        /// </summary>
        /// <param name="h"></param>
        /// <param name="lParam"></param>
        /// <returns></returns>
        private static bool EnumWindowsProc(IntPtr h, int lParam, string account, string pwd)
        {
            //改變帳號
            SetCursorPos(900, 530);
            SetForegroundWindow(h);
            SendMessage(h, 0x000C, IntPtr.Zero, account.ToString());

            //移動鼠標到登錄按鈕
            SetCursorPos(1090, 645);
            SetForegroundWindow(h);
            mouse_event(MOUSEEVENTF_LEFTDOWN | MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
            return false;
        }