I know there aren't many classic boards left that still intend to import, but the classic importer needs some updating.
Member Groups need updating, it doesn't work since 7.3 (I know we can do some manual mysql updates, but that's a bit scary when there's nearly 50k members to update).
It threw a "class html not present" error, apparently that has been changed in recent versions. The current importer won't even begin with that error in place.
There's a few other errors noted in this forum.