I went to http://test.musicbrainz.org/release/add and looked up an artist, entered a title and clicked on "edit note" and got:

Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "Attribute (params) does not pass the type constraint because: Validation failed for 'HashRef' with value undef at /usr/local/share/perl/5.8.8/HTML/FormHandler.pm line 857

when I did it again to reproduce it, I got:

Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "Could not create error

$VAR1 =

{ 'release_id' => 0, 'position' => 1, 'tracklist_id' => undef }

;

Attribute (tracklist_id) does not pass the type constraint because: Validation failed for 'Int' with value undef at /home/mbserver/musicbrainz/mb_server-next/script/../lib/MusicBrainz/Server/Edit/Medium/Create.pm line 35