? block.admin.inc.patch
Index: modules/block/block.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/block/block.admin.inc,v
retrieving revision 1.83
diff -u -p -r1.83 block.admin.inc
--- modules/block/block.admin.inc	8 Jul 2010 03:41:27 -0000	1.83
+++ modules/block/block.admin.inc	17 Jul 2010 02:31:20 -0000
@@ -502,6 +502,11 @@ function block_add_block_form_submit($fo
  * Menu callback; confirm deletion of custom blocks.
  */
 function block_custom_block_delete($form, &$form_state, $module, $delta) {
+  // We can only delete custom blocks, not blocks provided by other modules.
+  if ($module != 'block') {
+    drupal_not_found();
+    drupal_exit();
+  }
   $block = block_load($module, $delta);
   $custom_block = block_custom_block_get($block->delta);
   $form['info'] = array('#type' => 'hidden', '#value' => $custom_block['info'] ? $custom_block['info'] : $custom_block['title']);