Problem with KApInspect Lib

Hi,
when I link to the KapInspect lib I get the following error at runtime:

TypeError: Error #1007: Tentative d'instanciation sur un élément non constructeur.
at mx.preloaders::Preloader/initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\preloaders\Preloader.as:253]
at mx.managers::SystemManager/[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1925]" rel="nofollow">http://www.adobe.com/2006/flex/mx/internal::initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1925]
at mx.managers::SystemManager/initHandler()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:2419]

It's a Flex 3 app, being built in Flash Builder 4. I tried linking just the loader, I got the same error too.

More generally I've noticed there are some Flex projecs where Kap Inspect can't be linked to, and some others where it works...

Any idea what is going on?
Ariel