Fortune plugin get error

hi there.
i’m using fortune plugin in order to display random quote into page. I install, set configuration, create quotes file and put {{fortune}} globen variable on my page, but i get an error. Whatever page i open, i get this error.
Debug infos:
on this line
return $this->getRandomQuote($dir .$files[$i]);
saying: “Undefined variable: quotes”
Anyone can helpme? what is missing?