In restricted_content.module, on line 171:

171: 'restricted_content_message_anon' => t('Please register for a user account to view this !token-type-name.', array('!token-type-name' => module_exists('token') ? '[type-name-lower]' : t('content'), '!token-register' => module_exists('token') ? '[site-url-register]' : url('user/register'))),

The variable [site-url-register] should actually be [site-register-url].