=== modified file 'modules/user.module'
--- modules/user.module	
+++ modules/user.module	
@@ -859,7 +859,7 @@
 }
 
 function user_login_validate($form_id, $form_values) {
-  if (isset($form_values['name'])) {
+  if (!empty($form_values['name'])) {
     if (user_is_blocked($form_values['name'])) {
       // blocked in user administration
       form_set_error('login', t('The username %name has been blocked.', array('%name' => theme('placeholder', $form_values['name']))));