@marikane - You may need to contact your web hosting service to have them ensure your WordPress database user has the ALTER privilege. If it does not, have them add it, then if you roll back to NextGEN 2.0.40 (see this article for assistance: http://www.nextgen-gallery.com/how-to-rollback-a-version/) you should be able to re-update from there and your galleries will re-appear (if this is indeed the issue at hand).
- Cais.