I would suggest you check your vb
and set cookies as follows
cookie path /
cookie prefix is bb by default and set in your config.php file of vbulletin in the includes directory
cookie domain .domain.com
Now in Photopost view the settings table via phpmyadmin and set settings 171-173 to the correct cookie settings you just set for vb
In your Photopost config-inc.php file is the variable $vblicense and must be set to the correct vb
license number not customer number to properly authenticate people.