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/timthumbNbGPGD

Query String : src=http://automotomarco.it/gestione/imageGallery/098720500_1531404974.jpg&w=900&zc=1
TimThumb version : 2.8.13