qvtkwidget crashes when it is used inside a slot, please help

[Adem]

Hi all,

I have a strange problem regarding the behaviour of QVVKWidegt.

In my GUI I used a widget which is promoted to qvtkwidget inorder to visualize a 3D image.
I want the visualisation to start when I click a button (okbutton), for that, I have made signal slot connection as follows:
connect(ui->okButton, SIGNAL(clicked()),this, SLOT(VisualizeVolumes);
my code is built without any error however when I click the okbutton, I got an access violation at runtime.

When I call VisualizeVolumes as function(without slot)it works fine and even if I do the visualisation just after line ui->setupUi(this), it works as well.The crash happen only when I try to put VisualizeVolumes as slot.

I am a newbie to qt so please can you help? I am really stack and could not move?

I have attached my files for your attention

I am using itk4.4.2 vtk6 and Qt4.8.5
Thanks,
Adem