It sounds like your HandleClient.Comm.StatusChangehandler(UpdateGUI);
call is consuming the errors or something higher level is catching them. Have you tried to break pointing and stepping through the code?
In order to update controls from different thread, you need to Invoke the changes on your main thread.
Please see this question as it may help you out more. How to update the GUI from another thread in C#?
If you are using WPF, then it is done slightly differently and need to call Dispatcher.Invoke in order to update.
I hope this helps you out. It really does sound like your errors are being consumed without your knowledge.