Help rectifying errors formed during GUI building

Hi,

I'm doing a project on "Multi Camera Surveillance System by MERL". I've started the project with object tracking using gaussian mixture model and live histogram. I'm trying to incorporate these code into a GUI interface. Now I've been able to start and stop the internal webcamera.

Then I've used a 'pushbutton' as 'Track' which tracks the object. The problem arises here. I'm using Computer vision inbuilt functions for object tracking. So, when I paste the same code into my 'pushbutton_callback' function, I get a error.

The same happens when I try to see live histogram on GUI....Can you please help me?