Not showing ad, cause to wdca_not_placed css class

Hi,
I'm trying to get this plugin wotking, but it seems there is a lot of problems...

Finally I get it on html side, but it is hidden due to this class: wdca_not_placed

Why is this class there and how to remove? I don't want to force it through css 'cause there is a reason for this class to exist, but there is a lack of documentation on this (and other plugins too).

You can see the problem here: http://www.ilcommercialethesalesman.com/community/pillole-di-formazione/2012/01/sfida-o-salto-nel-buio.html (end of post) and the settings in the screenshot

Thank you for your support.
Federico