As you are aware, I had trouble linking the two programs, incorrectly putting in the User Registration System as phpBB and not phpBB2.
I edited the settings database and changed the Registration system to phpBB2 but continued to blow up.
I went back in and changed phpBB2 back to the original photopost and things work (but of course the two user files are not shared)
The only other setting I changed was the forum main directory:
I changed it from the default of http://www.domain.com/forum
to the actual location http://www.mysite.com/phpbb
but I do not see an error in what I keyed there.
So I am back to square one.