This problem was listed here, I can't find it now to link to it. (I'll try and find it later when I have a bit more time).
Your right it revolves around group_id.
You need to change $aro_group->group_id to $aro_group->id in some of the files.
Important thing I forgot was to change the files contained in the template I was using, so it didn't work at first. But its working now. Members can access the restricted boards as normal.
The files I changed were;
view.php
showcat.php
listcat.php
fb_sub_category_list.php
These were in the template directory of the template I'm using
You also need to change fb_pdf.php in the sources directory.
I'm using Joomla 1.5 stable and Fireboard 1.0.4
Paul
www.btka.org.uk