Just updated nextgen gallery to 2.0.17. I was using the hack described by mvandemar in this thread http://wordpress.org/support/topic/plugin-nextgen-gallery-nextgen-gallery-open-album-in-lightbox
Now I get [Not a valid template] as an answer on the page; of course I check that everything was alright as described in the hack. Plus Gallery -> Options -> Effects where I added this code: rel="prettyPhoto[%GALLERY_NAME%]" doesn't exist anymore.
Anyone else with this problem? If anyone could communicate with mvandemar maybe he has a solution.
Thank you all