On www.sarkinovic.nl/index.php/7-suco/1-wie-is
movies are in images/videos
I tested with mp4 and wmv movies.
Code I used is {mp4}suco{/mp4} and {wmv}suco{/wmv}
Path in plugin setting :  images/videos
Somehow the movie is not loaded in the player. I even changed permissions to 755.
Using Joomla 1.6.3 and latest version Allvideos plugin.
What to do?

The problem is related to your video encoding.
In our demo site Allvideos works perfect with these video formats:
demo.joomlaworks.net/allvideos

It was indeed the way of encoding. Adobe media encoder did the job very well. Thank you.