In untrackTicket, are you freeing the memory pointed by obj (the Control) that you've added using ticketContainer.add(obj) ?
I suspect that the crash is happening at:
ticketContainer.removeAll();
removeAll() documentation says: Removes all of a container's controls and frees up their memory.
If you have already freed that memory, removeAll will try to delete an object that have already been delete and thus will crash.