This tile grabber was forbidden from downloading tiles by OSM administrators. They did not listen to any reasoning for allowing it to download tiles. The policy is that they block all tile downloaders, regardless of how it works.
If a tile layer does not matter, use another one, like MapQuest Open.
Now, to download tiles, JTileDownloader is the best option, because it is easy on a server, having delays between requests and downloading tiles in quadtile order. You will have to change User-Agent
string, and for that you'll need to recompile the project. Download the source code:
svn co http://svn.openstreetmap.org/applications/utils/downloading/JTileDownloader/trunk/ JTileDownloader
Then find TileListDownloader.java
in src/org/...
and find a string Agent
inside it. Replace JTileDownloader
with any other word, and then compile and run the new version with ant run
in JTD's root directory.
Note that you should not download too many tiles, that is, more than a couple thousand. If you need more, please install PostgreSQL and Mapnik and generate as many tiles as you like locally.