A TimThumb error has occured

The following error(s) occured:

The remote file is not a valid image. Mimetype = ''/home/users/p/popracy/www/239584/html/thumbs/cache1-5/timthumbvc08SF

Query String : cat=galeria_obiektu&src=http://img.popracy.pl/fotki_obiekty/5972/8rea9u_12.jpg
TimThumb version : 2.8.14