I've been working with Mp3tag off and on for about a month. I can't find this problem on the FAQ. I was using V2.73, and today upgraded to 2.74a. I've been having intermittent problems accessing Discogs - getting a error connecting to server - 401 error. Sometimes it would be ok, sometimes not. accessing Amazon seems to be ok, Freedb seems ok.
Well it seems searching for "discogs 401" won't work, or maybe because I was searching FAQ and not Forum. So I did find that this has been an on going problem with Discogs. I tried the suggested fixes, but it didn't help much.