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/timthumb5skmWV

Query String : w=640&zc=1&s=1&src=http://www.gitav.com/pics/768.jpg
TimThumb version : 2.8.13