Select featured image

Hello,

I checked a lot of topics, ie.
http://wordpress.org/support/topic/featured-image-stops-working-with-wp-35

But unfortunately I cannot select the featured image from the Nextgen gallery, I see menu/button to use for it only the uploaded files from the media library. Since I should set up the featured image for more than 100 posts, I cannot upload new files for this.

Please be so kind and inform me, what make I wrong?

Thank you very much,
Andrea

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