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/timthumbQwuP6L

Query String : src=http%3A%2F%2Fwww.campeggio.it%2Ffoto%2Fsistemazioni%2Fapp.ti+piano+terra3%281
TimThumb version : 2.8.13