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/timthumb6hRVBQ

Query String : w=680&zc=1&a=c&src=http://www.raisgerbi.it/gestione/uploads/photo/68974_10343657_10203230212748325_7589525346208558025_n[1].jpg
TimThumb version : 2.8.13