I actually managed to do a restore from UBB.Classic too which went a lot smoother. Still, there are some errors in the import scripts. For example when no categories are set, it will not fetch the default 'general' category ID and therefore the import of the Forums will fail. This issue is also present in the UBB.Threads 6.5.5 importer.

Apart from this, I managed to import some older 6.x databases into the 6.5.5 version, but I do NOT succeed in upgrading it to 7.4.2 after that. Everything works EXCEPT for the post import (oh and the 'last post' for each forum), which failed / stopped (no errors) after say 200-odd posts (of the 120.000 or so). It was really late so I just restored the 6.5.5 version and have that running.

I've been longing for another feature though... make it so people can log in and see their messages or any extra Forums they are allow to see, but not actually change anything (add posts, change profile, update this and that). So people would just be able to log in and read. In this restored archive it would mean they can virtually log in and see their old messages (nostalgia... hah...), but not do any changes to this 'dead' Forum. For now I just crippled the login code so login is impossible.