Categorie link is empty in each story

[Juju66]

I have a problem on my pligg site : i'm using Digital Nature and pligg 0.90.
When i submit a story, i choose a category. But, when the story is publish, the category does not appear I just see :
Category: That's all

But, if i click in the category in the sidebar, i can see the story...

I hope you can understant me, my english level is dramatic.

Thank you.