OK, I found the fix from a previous thread
I had posted in the last time I tried to upgrade vbulletin to 3.5.0 this past summer:
Vb 3.5.0
This really makes me feel dumb. But I'll leave my ignorance on display here in case anyone else can benefit from it. Now its on to upgrading Photopost to the current release!
Cheers. -- Rik
ps: I was all about the following:
in header-inc.php find this
require_once('./includes/functions_showthread.php');
replace with
require_once('./includes/class_postbit.php');