I can your not help when you send me not a answer:
Is this a new installed 1.9 release, or has you moved it from a older Joomla (and jD) release to 2.5?
I understand not, what the user turminator has to do with your problem. So i have moved your post in a new thread.
Please activate for a test the debog option in your global config and try it again.
Post then here the viewed error.
Your first post:
Jdownloads Joomlart does not work with the themes. Overlap with the themes of Joomlart.
So here has jDownloads worked? But only a layout problem here?
Sorry but i need more and exactly informations. Otherwise i can not help you.