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/timthumbDG4joG

Query String : h=250&src=http%3A%2F%2Fwww.campingpuntala.it%2Fcover_immagini%2Fit%2Fvacanze-toscana%2F13667644870.26196289.jpg&w=670
TimThumb version : 2.8.13