Error "Audience not valid" when using TokenProvider.CreateSimpleWebTokenProvider(token)

When using TokenProvider.CreateSimpleWebTokenProvider(token) for aSubscriptionClient used with a MessagingFactory, I get a 401 error with the following information:

• The token provider was unable to provide a security token while accessing 'https://<mynamespace>-sb.accesscontrol.windows.net/WRAPv0.9/'. Token provider returned message: 'Error:Code:401:SubCode:T2002:Detail:Audience not valid.:TraceID:6d345761-a7f8-47c7-9424-462ace879cf3:TimeStamp:2014-07-03 12:55:01Z'.
  

But that doesn't happen when using TokenProvider.CreateSharedSecretTokenProvider(issuerName, issuerKey) 

The issuer has both a password and a key. The ACS token request is valid - I get it with the following code:

        static string GetAcsToken(string serviceNamespace, string issuerName, string issuerSecret)
        {
            var acsEndpoint = "https://" + serviceNamespace + "-sb.accesscontrol.windows.net/WRAPv0.9/";

            // Note that the realm used when requesting a token uses the HTTP scheme,
            // even though calls to the service are always issued over HTTPS.
            var realm = "http://" + serviceNamespace + ".servicebus.windows.net/";

            NameValueCollection values = new NameValueCollection();
            values.Add("wrap_name", issuerName);
            values.Add("wrap_password", issuerSecret);
            values.Add("wrap_scope", realm);

            WebClient webClient = new WebClient();
            byte[] response = webClient.UploadValues(acsEndpoint, values);

            string responseString = Encoding.UTF8.GetString(response);

            var responseProperties = responseString.Split('&');
            var tokenProperty = responseProperties[0].Split('=');
            var token = Uri.UnescapeDataString(tokenProperty[1]);

            Console.WriteLine("Token: " + token);
            //return "WRAP access_token=\"" + token + "\"";
            return token;
        }