I'm surprised its been this long and the issue hasn't been resolved. I've been using the following as a workaround in order to queue up replay downloads in conjunction with a download manager, so I may as well share:
It is possible to get direct replay links to download through a browser, which you can find using either the dotabuff website, or a packet sniffer.
Note: There is probably a simpler method, but I have no idea how dotabuff gets replays from match IDs, and the web API (which could easily be used to script up downloads for match IDs) is never working.
For most pub games; you should be able to put the match ID in dotabuff and it will give you a replay link at the top right corner of the match details page. If the download link doesn't work, the match is probably just unavailable (unrelated to error 206).
For tournament, private, and pub games where dotabuff cannot find the match ID; you will need to use a packet sniffer. This guide will show my method using Wireshark, an open source packet sniffer.
1. Get Wireshark and start the program.
2. In the capture section on the main page, ctrl+select all the interfaces listed and click start.
3. Enter the following filter:
http.request.uri contains "/570/"
and hit apply. This should be remembered in the list, so in the future just click the drop down box and select it.
4. All that screaming text should now be silent, time to start up Dota 2.
5. Simply open up the match details of which ever replay you wish to download, where it shows the download link. You don't need to attempt to download the replay.
6. Alt-Tab back into Wireshark, and it should have found some HEAD packets, which are used by Dota 2 to confirm whether or not a replay exists. The correct packets will show a .dem.bz2 file in the info section.
7. Select the packet, and in the information section below, click to unravel the Hypertext Transfer protocol section, and you should have a replay link you can double click. The end result should look like this:
Once you have the replay, extract the .dem.bz2 file (you will need a program like 7-zip or winrar) to:
Steam\steamapps\common\dota 2 beta\dota\replays\
and remove the second number so that the filename is the match id, followed by .dem (i.e 59649229.dem for match id 59649229)
Hope that helps any other poor soul suffering from error 2