I see a number of other complaints about problems retrieving info and cover art from Discogs, but none of them match my symptoms. I get the following error message:
"Failed to authenticate using OAuth (1) >> -2146893018: 2148074278: The message received was unexpected or badly formatted."
This has been going on for at least a week. I get the same error message no matter what track or album I submit, and no matter whether or not I'm logged into Discogs with my web browser.
Seems to me that it may have worked once only, just after I registered at Discogs a few weeks ago, but I'm not certain about that.
This is using Mp3tag 2.84a on Windows XP SP3.
P.S. - I really miss the Amazon integration. Not only was it pretty seamless, but the artwork was almost always of good quality, and the size was just right for me (500 or 600 pixels square). Discogs seem to be of lower quality in general, and the image size varies a lot.