为什么向虚拟机发送鼠标点击消息失败？

[zxhn001]

我向虚拟机发送鼠标点击消息，看上去有点击的动作，但不产生点击的效果，是怎么回事？
delphi代码：
SendMessage(formh, WM_MOUSEMOVE,MK_LBUTTON,MAKELPARAM(321,477));
sleep(500);
SendMessage(formh, WM_LBUTTONDOWN,MK_LBUTTON,MAKELONG(321,477));
sleep(500);
SendMessage(formh, WM_LBUTTONUP,MK_LBUTTON,MAKELONG(321,477));