What is Reason For EikCtl Panic 4

Hi All

i am Trying to Implementing the Custom Control For ListBox,
The Build was Successful, But While Runnig the Application I am Getting the EIKCTL Panic 4.
i Debuged the Code it Giving the Panic at Constructl. I searched in the Forums For EIKCTL Panic 4 but i did not get any Help, Could Any Body Tell Me Why I am getting the Panic, What Is the Reason For This Panic

Here Is the My Sample Code
CCustomListBox::CCustomListBox()
:CEikColumnListBox ()
{
}

void CCustomListBox::ConstructL(const CCoeControl* aParent, TInt aFlags)
{
CEikColumnListBox ::ConstructL(aParent, aFlags);// I am Getting the Panic Here
}

void CreatListBoxL()
{
CCustomListBox* iListBox = new (ELeave) CCustomListBox();
iListBox->ConstructL(this,
EAknListBoxSelectionList);
iListBox->SetListBoxObserver(this);
}