problem with mgd_list_topics

Hi,

I have some have problem using midgard function... I hope someone can help
me out here.
I have 2 topic in midgard. One is topic named "ttgkami" with topic id 169
and the other topic is "sahabat" with topic id 160. What I'm trying to do is
getting list subtopik under those two topic. Firs thing I do is using
mgd_list_topics()

For the topic ttgkami :

$ttgkami_topic = mgd_list_topics(169);
echo "$ttgkami_topic" //with output Object like I expected 



But for topic sahabat :

$sahabat_topic = mgd_list_topics(160);
echo "$sahabat_topic"; /* strangely give me error "Fatal error: Call to a
member function on a non-object in ROOT on line 992" */


Does anyone can give me a hint why is sahabat topic give me such error?
(I'm using midgard 1.5)

Thanks,

-- 
Uung H.R Bhuwono


Hail The Revolution...!!!!