Ashley
On install we ask two things your vbulletin license number and the vbulletin cookie prefix. To get into admin area these need to be correct.
If your getting logged out of vbulletin I would tend to think your license number is incorrect. However check both.
In your config-inc.php file of Photopost you can enter the proper license number where asked. You can find the vbulletin license number and cookie prefix in the vbulletin config.php file in the includes directory of
vb. Usually the cookie prefix is bb. The license number is at top of file
To update the cookie prefix you can use phpMyAdmin in your control panel to issue this query
UPDATE pp_settings SET setting='bb' WHERE id=182