Problem two forms using Qt and OpenCV

[romeo.rbw]

Hi...
I appreciate if you give me some suggestion of this because I am still new comer in Qt world.
I use Qt in Windows. I made a MainWindow contain a QWidget. That QWidget display a capture from WebCam, I used OpenCV. That was already work well. Now, I make a pushbutton in the MainWindow and hope that create a new Form when clicked. The form already create well and displayed however if I push a button only once but it appeared two forms (double). In the new form I also made a QWidget and hope can display the same thing like in the QWidget in my mainWindow. But the second form only display a black color until now.
The error message is:
Object::connect: No such slot FormDisplay::onImageReceive(cv::Mat&)
Object::connect: (sender name: 'MainWindow')
Object::connect: (receiver name: 'FormDisplay')

Here are my code, sorry about my English.
main.cpp
@
#include <QtGui/QApplication>
#include <QObject>

#include "mainwindow.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow *dialog = new MainWindow;
//----------------
FormDisplay second;

QObject::connect(dialog, SIGNAL(sendImage(cv::Mat&)),
                 &second, SLOT(onImageReceive(cv::Mat&)));
//----------------
dialog->show();

return a.exec();

}
@

mainwindow.cpp constructor and function:
@
#include "mainwindow.h"
#include "formdisplay.h"
#include "ui_mainwindow.h"
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <qmath.h>

#include <QTime>
#include <QPainter>
#include <vector>

using namespace cv;
using namespace std;

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);

connect (ui->displayButton, SIGNAL (clicked()),this, SLOT(on_displayButton_clicked()));

}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::on_displayButton_clicked()
{
formdisplay=new FormDisplay();
formdisplay->show();// showFullScreen();
formdisplay-> raise();
formdisplay-> activateWindow();

emit this->sendImage(mOrigImage);

}
@

mainwindow.h
@
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <formdisplay.h>
#include <QMainWindow>
#include <QLabel>
#include <QTime>
...
using namespace cv;
using namespace std;

class Form1;

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

private:
...
private slots:
...
void on_displayButton_clicked();

signals:
void sendImage(cv::Mat &image);

private:
Ui::MainWindow *ui;

FormDisplay   *formdisplay;

//cv::Mat                     mOrigImage;
...

protected:
void timerEvent(QTimerEvent *event);

public:
cv::Mat mOrigImage;
FormDisplay second;
};
#endif // MAINWINDOW_H
@

formdisplay.h :

@
#ifndef FORMDISPLAY_H
#define FORMDISPLAY_H

#include <QWidget>
#include <QMainWindow>
...

namespace Ui {
class FormDisplay;
}

class FormDisplay : public QWidget //QMainWindow //
{
Q_OBJECT

public:
explicit FormDisplay (QWidget *parent = 0); //(QMainWindow *parent = 0);
~FormDisplay();

private:
Ui::FormDisplay *ui;

public slots:
void onImageReceive(Mat &image);
};

#endif // FORMDISPLAY_H

@

formdisplay.cpp:
@
#include "formdisplay.h"
#include "ui_formdisplay.h"

FormDisplay::FormDisplay (QWidget *parent) : // ??(QMainWindow *parent) :
QWidget(parent), // ??QMainWindow(parent),
ui(new Ui::FormDisplay)
{
ui->setupUi(this);
}

FormDisplay::~FormDisplay()
{
delete ui;
}

void FormDisplay::onImageReceive(cv::Mat &image)
{
//ui->FormDisplay->viewerDisplayCV->showImage(image);
ui->viewerDisplayCV->showImage(image);
}
@

The viewerDisplayCV have promoted class from openGL viewer. It already done well in the MainWindow.

any suggestion and help would be very appreciated. Thank you in advance.
-romy