So your saying you installed Photopost as an internal install then you wanted to move to IBP 2.0? You post is a little confusing? Have you installed it to use IBP 2.0?
If you have installed Photopost as a internal and then are switching to IBP your usergroups tables will not match. You can use PHPMYADMIN and delete all entries from your photopost usergroup tables except administrators. Set that entry to have a groupid of 4 and make sure cpaccess is set to 1. If you had an internal install the administrators entry is 5 that is why you dont have access to admin. See what I mean
I am assuming you also already changed the settings table entry 41 to a setting of ib2 and changed setting 83 to any table prefix of ib2 and changed your config file database entry.