Error on generating the code

Hi,
This is an interesting one.
I did create a layout for my notebook panel. This notebook will be on the
dialog for the property pages.
So in the tree I only have Application and my panel class.

However, when I try to generate the code for this panel I got an error

[quote]
Please select a top window for the application
[/quote]

What can I do to generate the code for my panel?

Thank you.