The recent version of dkret3 is not WP2.6 compatible.
I already uploaded a fixed version which should be online as soon as it is reviewed.
You can make the needed changes yourself:
in line 359 change:
add_filter('get_comments_number', 'comment_count', 0);
to:
if(function_exists('separate_comments') )
add_filter('get_comments_number', 'comment_count', 0);
By the way: If you already use WP2.7 you won't see any error at all. dkret3 works like charm with this version.