The files must be unzipped when installing in ATV>XBMC. Think your message occurs when you put an already zipped folder to your ATV.
I´m trying to figure this out myself. I´ve downloaded a zip file to my mac, used Cyberduck to transfer the file to ATV, but the file don´t show up in XBMC. Any hints on how to get the files up in the ATV (XBMC) menu?