Discogs are making further changes to their API such that querying tag data now requires user authorisation ie. you need to set up an account on discogs and authorise MusicBee to retreive tag data.
I will add support for this but because of the authorisation steps involved i am going to move the functionality to a plugin and will remove native support within musicbee itself.
I will provide the plugin and the instructions separately in the plugins topic later. By using the plugin and authorising MusicBee on your discogs account you will lose no tagging functionality and also gain back discogs artwork retrieval that was previously removed (however for artwork there is a 1000 limit on requests per application (musicbee, mp3Tag, etc) for all users per day which i imagine will be quite constraining)