Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 21877)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -203,7 +203,7 @@
 	 * @param string $password User's password.
 	 * @return mixed WP_User object if authentication passed, false otherwise
 	 */
-	function login($username, $password) {
+	function login( $username, $password ) {
 		// Respect any old filters against get_option() for 'enable_xmlrpc'.
 		$enabled = apply_filters( 'pre_option_enable_xmlrpc', false ); // Deprecated
 		if ( false === $enabled )
@@ -217,10 +217,10 @@
 			return false;
 		}
 
-		$user = wp_authenticate($username, $password);
+		$user = wp_authenticate( $username, $password );
 
-		if (is_wp_error($user)) {
-			$this->error = new IXR_Error(403, __('Bad login/pass combination.'));
+		if ( is_wp_error( $user ) ) {
+			$this->error = new IXR_Error( 403, $user->get_error_message() );
 			return false;
 		}