Index: wp-admin/edit-tags.php
===================================================================
--- wp-admin/edit-tags.php	(revision 18731)
+++ wp-admin/edit-tags.php	(working copy)
@@ -9,6 +9,8 @@
 /** WordPress Administration Bootstrap */
 require_once('./admin.php');
 $tax = get_taxonomy( $taxnow );
+if ( !$tax )
+	wp_die( __( 'You attempted to edit an item that doesn’t exist. Perhaps it was deleted?' ) );
 if ( !current_user_can( $tax->cap->manage_terms ) )
 	wp_die( __( 'Cheatin’ uh?' ) );