이렇게 하시면 되는데...
왜 이런게 되는지는 함보세요

procedure LabelMOUSE_Sender(Fname : TForm ; FRMLabel : TLabel);

var
        Pt      : TPoint;
begin

        Application.ProcessMessages;

        Pt.x := FRMLabel.Left + (FRMLabel.Width  div 2);
        Pt.y := FRMLabel.Top  + (FRMLabel.Height div 2);

        Pt := Fname.ClientToScreen(Pt);
        Pt.x := Round(Pt.x * (65535 / Screen.Width));
        Pt.y := Round(Pt.y * (65535 / Screen.Height));
       {Move the mouse}
        Mouse_Event(MOUSEEVENTF_ABSOLUTE or
                    MOUSEEVENTF_MOVE,
                    Pt.x,
                    Pt.y,
                    0,
                    0);
       {Simulate the left mouse button down}
        Mouse_Event(MOUSEEVENTF_ABSOLUTE or
                    MOUSEEVENTF_LEFTDOWN,
                    Pt.x,
                    Pt.y,
                    0,
                    0);

       {Simulate the left mouse button up}

        Mouse_Event(MOUSEEVENTF_ABSOLUTE or
                    MOUSEEVENTF_LEFTUP,
                    Pt.x,
                    Pt.y,
                    0,
                    0);

end;