A TimThumb error has occured

The following error(s) occured:

The remote file is not a valid image. Mimetype = 'text/html' File = /var/www/html/timthumb/cache/timthumbE7gWBI

Query String : w=860&zc=1&s=1&src=http://www.campingilgabbiano.it//gestione/uploads/photo/87156_IMG_4527.JPG
TimThumb version : 2.8.13