[OmerE]

In the patch file included here I neglected to add one required line
which is required in order to create a temporary column in the attachment
table during the upgrade process.

In impex/systems/phpBB2/001.php, around line 89, and AFTER you
use the patch file, find this:

                                '13'    => array('post'                 =>  'importpostid')

Replace with:

                                '13'    => array('post'                 =>  'importpostid'),
                                '14'    => array('attachment'                 =>  'importattachmentid')

If you're in the middle of the process, just add a BIGINT colum
named 'importattachmentid' to the attachment table.