[Plugin: NextGEN Gallery] Thumbnails problems

Hi,

I have a problem with the thumbnails of the images of the gallerys of NextGEN Gallery. The thumbnails doesn’t appear, here you can see some examples:

http://media.enfilo.com/?page_id=134

http://media.enfilo.com/?page_id=219

I’m using NextGEN Gallery 1.7.4

http://wordpress.org/extend/plugins/nextgen-gallery/