How to debug vaadin source code

Hi all,

I got an Exception from Vaadin a GUI component.
I’d like to set some debug points in the Vaadin source code.
I use Netbeans ( usually I use Eclipse) and I can see the Vaadin source code but when I try to set some debug points Netbeans warned me that I miss some debug information.
Any suggestion ?
Cheers.

                  Stefano