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/timthumbN6p19G

Query String : w=680&zc=1&a=c&src=http://www.raisgerbi.it/gestione/uploads/photo/2140_13716101_1562139167429018_3340165891893203461_n[1].jpg
TimThumb version : 2.8.13