It depends on the tracker & the torrent. If the tracker is actually down then the only 2 ways you could get the file is by DHT or if your client supports PEX.
If the tracker is up and the torrent won't download it's probably due to there not being any seeds. Both of the mentioned errors seem to be tracker related. Can you specify which torrent your having trouble with? desioner
They could either be blocking certain ip ranges, blocked port if you're behind a firewall, sign up required or ISP related. In anycase they all do work and can sometimes be fixed if you redownload the torrent files.