Attempt to add duplicate artist via Release Editor causes Internal Server Error

After entering all the details for a new release, I'm getting this error message:

Error:

Caught exception in MusicBrainz::Server::Controller::ReleaseEditor::Add->add "No artist was created for Tony Murena at /home/musicbrainz/musicbrainz-server/script/../lib/MusicBrainz/Server/Wizard/ReleaseEditor.pm line 832."

Stack trace:

line 832 MusicBrainz::Server::Wizard::ReleaseEditor
line 777 MusicBrainz::Server::Wizard::ReleaseEditor
line 93 MusicBrainz::Server::Wizard::ReleaseEditor
line 23 MusicBrainz::Server::Controller::ReleaseEditor::Add
line 270 MusicBrainz::Server

Request data:

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

{ 'save' => 'Enter edit', 'edit_note' => 'from original 2CD box', 'wizard_session_id' => '0.17556817441961' }

};

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