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/timthumb7eK8sK

Query String : w=680&zc=1&a=c&src=http://www.raisgerbi.it/gestione/uploads/photo/26179_545321_460614860648179_773608883_n[1].jpg
TimThumb version : 2.8.13