[Plugin: Recent Post Slider / Smooth Slider] sliders don't appear anymore

Hi everyone,
I am using the Weaver II theme on my website https://www.bhutan-research.org. On my frontpage I always used a slider for the latest articles published, but recently, these sliders do not appear anymore. I do not get any error messages and I cannot say exactly since what time it does not work anymore (I did not update my site for some time, but I guess its since the wp 3.5.1 update).
I have tried different plugins, i.e. Recent Post Slider and Smooth Slider, deleted them and installed them again, but nothing seems to work. I usually integrate them as a widget in the site-wide-top-widget-area, and also tried using the shortcode.
However, when inspecting the elements of the frontpage with my browser (Opera) the respective code for the slider is there.
I would be really grateful, if someone had an idea as to where the problem might be!