Index: includes/display-edit.inc
===================================================================
--- includes/display-edit.inc	(revision 170)
+++ includes/display-edit.inc	(working copy)
@@ -1505,6 +1505,7 @@
  * AJAX entry point to configure CSS for a pane.
  */
 function panels_ajax_configure_pane_css($cache, $pid = NULL) {
+  ctools_include('content');
   if (empty($cache->display->content[$pid])) {
     ctools_modal_render(t('Error'), t('Invalid pane id.'));
   }