QComboBox problem

[SteveH]

Hi,
I've a recurring problem with QComboBox's causing a program crash.
I am using QCreator 0.9.2 RC1 and am building a QMainWindow which then calls a QIODevice class which then calls a QDialog class, the QComboBox's are in the QDialog class. If I use a QComboBox access like say ComboBox->setCurrentIndex(2) anywhere but in the function where the QComboBox is created then the program will crash when it reaches that point.
I built a minimal test program of the above layout which always worked but as soon as I add lots of elements the program will always crash.
Does anyone have a handle as to where I'm going wrong ???
A sample of the program is listed below with virtualy everything stripped out but still able to crash everytime.