Okay yep was gonna say you need to change your integration.
There would be two more steps to do as well. Using phpmyadmin you would need to edit the settings table entries 171-173 and set to the proper cookies for vbulletin most notably if you can not login to admin is the cookie prefix. It is by default bb (you can verify by looking at vb
config file) and change this setting to bb from phpbb2mysql
Next view the usergroups table and delete all entries except admin which you need to change the groupid from 2 to 6
You should then be able to login and you can refresh your usergroups