Help with 400 Bad Request

I'm attempting to write a client library to send ratings to MusicBrainz.
There is no existing client library for my environment (c#) that supports
sending ratings, so I am attempting to write my own.

Here's the info about my http request:

URL = http://musicbrainz.org/ws/2/rating?client=MyGrooves-0.0.1

Method: POST

Request Headers:
UserAgent = JmmRater/1.0.0 ( [email protected] )

Content Headers:
Content-Type = application/xml; charset=utf-8

Content:
<?xml version="1.0" encoding="UTF-8"?> <metadata xmlns="
http://musicbrainz.org/ns/mmd-2.0#">
                    <recording-list>
                        <recording
id="f5aec1b4-0162-489b-ad1a-2aeecebc7d8a">
                            <user-rating>4</user-rating>
                        </recording>
                    </recording-list>
                </metadata>

I am sending Digest authentication credentials.

When I send this, I am getting a status code of 400 Bad Request.
The content of the response is blank.

I'm not sure where to go from here.  Does anyone see anything above that
points to what I'm doing wrong?  If not, how can I debug this?

Thanks,
   Joe

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