I had received the same error when trying to download a torrent from a certain web site. I searched the site's forums for help, but instead of providing me with a solution a lot of people would say to switch to Azureus.
Nothing against Azureus (never tried it), but I like BitTornado. It has always worked for me. It has good speeds (better than other progs I've tried) it is super easy to use, doesn't have a whole bunch of unnecessary bells and whistles that I won't use and I rarely run into problems. Many thanks to Shadow for providing such a great program for FREE!
So anyway, after much searching I finally came across a solution posted by someone in a forum I visit.. These are the instructions he gave:
1. Use the external announce feature in advanced options.
2. Enter one of the tier 0 addresses listed under details ((http://...etc..
.) It's usually the first one. and omit the extra slash / after /tracker//.
3. That's it.
I did this and it worked.
No offense to Shadow, but I came across this solution before the one you recommend, which I didn't try because I had already fixed the problem.