[Mooff]

That doesn't look like a vb4-cms at all. Judgeding from the code i severly doubt it is one.

@Gamelobby
The wrong link to the articles has nothing to do with where the slider wants to save the images. Per default i'm asuming the content.php resides in the main http folder and not in a subfolder. Anyway, for that to work correctly

search in the php widget code

                //Build Array
                $article_neu = array();
                $article_neu['description'] = '<h2 style="font-weight:bold; font-size: 14px">'. $article['title'].'</h2><span>'. $article['previewtext'] .'</span> <a href="/content.php?r=' . $article['nodeid'] . '-' . $article['url'] . '">read on</a>';
                $article_neu['htmlcaptionname'] = 'htmlcaption' . $i ;
                $article_neu['picture'] = '<a href="/content.php?r=' . $article['nodeid'] . '-' . $article['url'] . '"><img src="'.$article['previewimage'].'" alt="" title="#htmlcaption'. $i . '" /></a>';

and replace with this code

                //Build Array
                $article_neu = array();
                $article_neu['description'] = '<h2 style="font-weight:bold; font-size: 14px">'. $article['title'].'</h2><span>'. $article['previewtext'] .'</span> <a href="/Forum/content.php?r=' . $article['nodeid'] . '-' . $article['url'] . '">read on</a>';
                $article_neu['htmlcaptionname'] = 'htmlcaption' . $i ;
                $article_neu['picture'] = '<a href="/Forum/content.php?r=' . $article['nodeid'] . '-' . $article['url'] . '"><img src="'.$article['previewimage'].'" alt="" title="#htmlcaption'. $i . '" /></a>';

As for the other question why the images do not show up. Can you please post the debug messages the slider puts out in debug mode?
As for checking how to find out whether fopen/ allow_url_open is active or not. I would have to google that aswell. Best is to ask your techadmin, since he is the guy who would need to activate it.

@Kr33p3r
I'll try to come up with a version on monday which pumps out a bit more debug to see what is going on there. Kinda lost right now.