Using the "Add cluster as release" plugin from Pickard, Musicbrains seem to have a problem adding this specific album, as I don't see this error on other albums.

The musicbrains webpage returns with:
------------------------------------------------------------------
Internal Server Error

Oops, something went wrong!

Error:

Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "Not an ARRAY reference at lib/MusicBrainz/Server/Wizard/ReleaseEditor.pm line 1593, line 17."

Stack trace:

line 1591 MusicBrainz::Server::Wizard::ReleaseEditor
line 314 MusicBrainz::Server::Wizard
line 131 MusicBrainz::Server::Wizard
line 95 MusicBrainz::Server::Wizard::ReleaseEditor
line 20 MusicBrainz::Server::Controller::ReleaseEditor::Add
line 338 MusicBrainz::Server
line 312 MusicBrainz::Server
line 339 MusicBrainz::Server
line 353 MusicBrainz::Server
line 398 MusicBrainz::Server

Request data:

$VAR1 = {
'query_parameters' => {},
'body_parameters' =>

{ 'mediums.0.track.-1.length' => [ '1044179', '975773', '879642' ], 'name' => 'Barren Land', 'mediums.0.track.-1.name' => [ 'Barren Land', 'Faith & Fear', 'Untold' ], 'artist_credit.names.0.artist.name' => 'Arcana XXII' }

};

Host: astro

URL: http://musicbrainz.org/release/add

We're terribly sorry for this problem. Please wait a few minutes and repeat your request — the problem may go away.

If the problem persists, please report a bug and include any error message that is shown above.

Please be sure to include the stack trace and request data shown above!
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Not sure if this is an error in the plugin or the Musicbrains database.