Why do I get 401 errors connecting to the Dynamics CRM Metadata service?

CrmAuthenticationToken token = new CrmAuthenticationToken();
token.OrganizationName = config.AppSettings.Settings["CrmTargetOrganisation"].Value;
token.AuthenticationType = 0;

MetadataService service = new MetadataService();
service.Credentials = System.Net.CredentialCache.DefaultCredentials;
service.Url = config.AppSettings.Settings["CrmMetadataServiceUrl"].Value;
service.CrmAuthenticationTokenValue = token;
service.UnsafeAuthenticatedConnectionSharing = true;