Topic: Some strange error...

At http://forum.pctipy.net/index.php , you can see that below "Internet" is

Warning: Invalid argument supplied for foreach() in /data/web/virtuals/865/virtual/www/index.php on line 160

Line 160 contains

foreach ($new_topics[$cur_forum['fid']] as $check_topic_id => $check_last_post)

Is it possible to fix this somehow? It doesn't affect other pages in any way, but it just doesn't look well...