When trying to submit a rating for a release via the webservice, for example,

POST http://musicbrainz.org/ws/2/rating?client=WebService-MusicBrainz-NGS-TestSuite-0.01
Content-Type: application/xml; charset=utf-8

<?xml version="1.0" encoding="UTF-8"?>
<metadata xmlns="http://musicbrainz.org/ns/mmd-2.0#"><release-list><release id="60952a6e-895e-4270-9bbe-f65a7c6035f8"><user-rating>100</user-rating></release></release-list></metadata>

the server responds with an internal server error. The relevant line within the html returned seems to be,

Caught exception in MusicBrainz::Server::Controller::WS::2::Rating->rating_submit "Can't locate object method "rating" via package "MusicBrainz::Server::Data::Release" at /home/musicbrainz/musicbrainz-server/script/../lib/MusicBrainz/Server/Controller/WS/2/Rating.pm line 63."

Submitting ratings for artists, labels, recordings, release-groups and works is fine.