Can't import nothing but users

Hey there,
It's been few days now that we're* with the head in the wall,

We are trying to import phpBB3 db into Drupal, we have phpass, bbcode, privatemsg, forum signature, upload_comment modules installed.
All fields are filled right (working on staging site, root is admin, use bbcode, the bbcode input format was made.

Importing started without any problem, users imported well (maybe 30 users only failed to import), but starting with importing forums into containers - nothing works! following this, the topics and the posts, none success importing.

If I remember right, the first importing succeed importing, but we used some settings that we wanted to change, so we rolled back the db, and since than it doesn't work (using the exact same db as in the first time (both the Drupal db and the phpBB db).

any ideas where we can start looking for the reason? we don't even have a clue where to begin looking!

Many thanks,
* We, the site's team.