Hm, at this time I have no installed JFusion to test but we can try test it on you site

Open file /plugins/jcomments/jcomments.avatar.php
Find line:
require_once(JPATH_ADMINISTRATOR .DS.'components'.DS.'com_jfusion'.DS.'models'.DS.'model.factory.php');
and add after it next:
require_once(JPATH_ADMINISTRATOR .DS.'components'.DS.'com_jfusion'.DS.'models'.DS.'model.jfusion.php');
Some lines below find:
$comments[$i]->profileLink = JRoute::_('index.php?mode=viewprofile&u=' . $avatars[$fusername]->user_id . '&jfile=memberlist.php&option=com_jfusion&Itemid=' . $Itemid);
and replace with:
$comments[$i]->profileLink = JFusionFunction::routeURL('index.php?mode=viewprofile&u=' . $avatars[$fusername]->user_id . '&jfile=memberlist.php&option=com_jfusion', $Itemid);
I hope it must fix described problem... Please try and say if it help...
JFusionFunction