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/timthumbjpecgC

Query String : w=680&zc=1&a=c&src=http://www.raisgerbi.it/gestione/uploads/photo/20039_11953228_965731093469884_729905452967286509_n[1].jpg
TimThumb version : 2.8.13