Thats probably blocked as well - all the products like websense, bluecoat etc have a giant list of site in their database and all the proxy avoidance sites are probably blocked.
Just insert a proxy address in the proxy port number and change port to 80. You're done. You can access any blocked website or blocked file extension.
E.g: proxy sever adress: vimuto.com
Port no.: 80
This method works for me.