If you've had to try two different paths, then are you certain you've got the correct path?
Another possible cause is if the users who uploaded them in vBulletin, can't be found in XenForo.
After you imported from vBulletin to XenForo you had to specify the name for your archived import log. The Photopost import configuration should ask you for this. Are you sure you have entered the correct log name?