error when using userlist

Hello,

I'm getting an error when trying to display the userlist.
Error: "Warning: Invalid argument supplied for foreach() in /customers/knightsrazor.be/knightsrazor.be/httpd.www/components/com_userlist/userlist.html.php on line 73".
The page can be found here: http://www.knightsrazor.be/index.php?option=com_userlist&Itemid=59

Any suggestions?
thx
Peter

It's not been tested with 1.5.

ok, thx for the quick reply 
But maybe the compatibility needs to be changed on this page: http://extensions.joomla.org/component/option,com_mtree/task,viewlink/link_id,364/Itemid,35/

Userlist has been made compatible with Joomla! 1.5 in legacy mode now. Upgrade to v2.5.

I get the same problems when my use list too long !