I am having this exact same problem, but my phpbb database is in the same place as my wordpress database. (_phpbb and _wordpress on my MySQL server).

Anyone figure this out?

[@netweb Keymaster 11 years, 8 months ago]

I moved your reply in this topic to a new topic as they are separate issues.

You shouldn’t have a problem with your setup if you follow the docs:
https://codex.bbpress.org/import-forums/