Hi Thom,
There are several forks of this plugin out there but what worked for me is editing layer.php and replacing:
if(count(@$this->content['navigation']['cat']) && qa_opt('useo_cat_title_nav_enable')){
with:
if(isset($this->content['navigation']['cat']) && count($this->content['navigation']['cat']) && qa_opt('useo_cat_title_nav_enable')){
and replacing
if (count(@$useo_tag_desc_list)) {
with
if (is_array(@$useo_tag_desc_list) && count($useo_tag_desc_list)) {
wherever they occur.
I hope it also works out for you. :-)