Nope I run on Photopost on PHP 5.0
Are you sure you properly switched everything to VB3 from UBBThreads? Something has to be set wrong if you get a blank page and without any type of error being displayed all I can do is stab in the dark here.
Double check all your database settings your config file etc and make sure they all point to the right tables prefix integration etc. Do your server error logs say anything