We rely on torrent tracker web sites in order to provide search functionality. Those web sites might be down or blocked by Internet Service Providers (ISPs).
If you see this error message, please try another provider by selecting one in a drop-down list next to the search button. If none of them works for you, then still can add torrents or magnet links from other sources. Here is a list of most popular trackers: http://torrentfreak.com/top-10-most-popular-torrent-sites-of-2013-130106/