What for a format has the downloaded style?
Generally, it should be a *.tar or *.tgz file. Try a style from the Plugin-Store: http://www.woltlab.com/pluginstore/
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KittBlog Stile - Ihr Kit für Stile, Software und Knowhow
Your kit for styles, software and knowhow
So, did you try it with a style in the Plugin-Store and did it work?
On the other hand, can you send my the style from psd resources so I can look if it's the right format inside the *.tgz?
Mit freundlichen Grüßen Best regards
KittBlog Stile - Ihr Kit für Stile, Software und Knowhow
Your kit for styles, software and knowhow