[Plugin: WP-dTree] dtree 3.5 not displaying categories on production environment

I have the following problem:
1- I installed WP-dtree on my local server, activated it, modified my categories to have a nicely organized tree.
All is working perfectly.
2- I then transfered the plugin file on the internet server, as well as the archives.php file of the theme and transfered the MySQL database from my local server to the internet server
3- Then on the internet server, categories are not displayed. I just have the “open all | close all” line. However when I look at the source code of the page, they are identical (expcept of course for url which on my local server points to http://localhost). The code with all categories is there, it looks like it is just not executed.

Plugins used on both side are exaclty the same, so I really don’t understand.

here is the URL : http://www.tozai-trek.com/archives-en/en/

Is there anything special to do on the server side, like some environment variable to modify to get the plugin to work?