A TimThumb error has occured

The following error(s) occured:

You may not fetch images from that site. To enable this site in timthumb, you can either add it to $ALLOWED_SITES and set ALLOW_EXTERNAL=true. Or you can set ALLOW_ALL_EXTERNAL_SITES=true, depending on your security needs.

Query String : src=http://www.zitbrno.cz/wp-content/uploads/2011/08/3503759302_1dc62cbf4e-300x225.jpg&w=70&h=65&zc=1
TimThumb version : 2.8