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/timthumbwLiiYp

Query String : src=http://www.campeggio.it/foto/sistemazioni/tende_attrezzate%20(3
TimThumb version : 2.8.13