A TimThumb error has occured

The following error(s) occured:

Curl returned: 403
The remote file is not a valid image. Mimetype = 'text/html' File = /var/www/html/timthumb/cache/timthumbOG5S8b

Query String : w=680&zc=1&a=c&src=http://www.raisgerbi.it/gestione/uploads/photo/44316_12540564_1035774833132176_6156836171766456658_n[1].jpg
TimThumb version : 2.8.13