Ticket #14296: 14296.diff

wp-includes/link-template.php

@@ -1342 +1342 @@
  * @param bool $previous Optional, default is true. Whether display link to previous post.
  */
 function adjacent_post_link($format, $link, $in_same_cat = false, $excluded_categories = '', $previous = true) {
-        if ( $previous && is_attachment() )
+        if ( $previous && is_attachment() && !empty($GLOBALS['post']->post_parent) )
                 $post = & get_post($GLOBALS['post']->post_parent);
         else
                 $post = get_adjacent_post($in_same_cat, $excluded_categories, $previous);