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/timthumbkYwcaC

Query String : src=http%3A%2F%2Fwww.gitav.com%2Fimg%2Fstrutture%2Fgallery%2Fosa%2F3.jpg&w=640&zc=1
TimThumb version : 2.8.13