I leeched a nos. of fresh L1 HTTP proxies with port - 9090, scanned with time out 5 sec. Most of them were Us proxies and had not been suspected as proxy IP. When I went to post to craigslist every time I found "The page cannot be displayed" both in IE and firefox. Same happened with backpage and kijiji but not with gumtree. Some time first page of CL was opened but could not proceed further. I wish to know the reason ( I have not much knowledge about proxy), please explain.