Urgent - How to get a reference to a Nested Datawindow within another Nested Datawindow???

Dear all,

I'm using PB 6.5.1. I have a report with the following layout:
Datawindow A contain Datawindow B, Datawindow B contain Datawindow C

And I want to get a reference to Datawindow C. However, I tried to use
GetChild() for Datawindow B. It retured -1. Thus, I also tried to get
another Datawindow D which is nested in Datawindow A and no nested
datawindow nested in it. Then, using GetChild is worked for this case. Am I
missing something?? is there any other way round?? Any ideas or suggestion
are welcome. Thanks in Advance.

Best Regards,
Andy Cheung