i put this code in the skin template file
---------------------
$Skin->container( NT_('last comment'),array(
'block_display_title'=>false
)) ;
-------------------------

and normally browse this page is ok , but when click the comment section and into the page, the comment section on this page will be trigger an error . the page URL somethings like this :"index.php/2008/04/25/guide_to_getting_your_z_visa_work_aamp_r?blog=5#c74888", and the error information detail below:
------------------------
An unexpected error has occured!

If this error persits, please report it to the administrator.

Go back to home page
Additional information about this error:
Requested Item does not exist!
-----------------------

i also trace the code, and found that in this condition , the file
-------------------------------
inc\_core\model\dataobjects\_dataobjectcache.class.php
-------------------------------

which include an function

------------------
function & instantiate( & $db_row )
-----------------

on this line

----------------
if( isset( $this->cache[$obj_ID] ) )
----------------

the value "$this->cache[$obj_ID] " is an NULL object . that means its will be return an NULL object on this function .

is it a bug ? or just i make some mistake in somewhere ?

my temporary solution , check if the value "$this->cache[$obj_ID] " is NULL . if yes, add a new obj into the cache .
---------------------------
$this->add( $this->new_obj( $db_row ) );
---------------------------
also check "add" function on this page .