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/timthumbFTZxuF

Query String : src=http://www.campingitalia.it/foto/strutture/734277_552781921409107_1303595921_n.jpg&zc=1&w=640&a=c&s=1
TimThumb version : 2.8.13