Index: content_crud.inc
===================================================================
--- content_crud.inc	(revision 2404)
+++ content_crud.inc	(working copy)
@@ -313,6 +313,7 @@
  *   The number of field instances deleted.
  */
 function content_field_instance_delete($properties) {
+  include_once('./'. drupal_get_path('module', 'content') .'/content_admin.inc');
   $number_deleted = db_query("DELETE FROM {node_field_instance} WHERE type_name = '%s' AND field_name = '%s'", $properties['type_name'], $properties['field_name']);
 
   $type = content_types($properties['type_name']);