additional info:
the problem I have is that as soon as I call an image from the gallery (in picture list) the image comes up but the whole screen blacks out immediately. I have set the mode to lightbox. If I disable WP-Slimbox, the image comes up, but I cannot go to the next one, I have to go back with the browser. If I now choose fancybox, everything runs fine. If I re-activate WP-Slimbox, even with Fancybox set, the problem re-appears. I am using WP 3.6, Nexrgen beta 2.0.2 and WP-Slimbox 1.1.2