For anyone trying to import Polls in a newer version of XF and getting "the field 'multiple' does not exist", it's because XF no longer has a "multiple" field on Polls. They changed it to "max_votes".
You can fix that by editing vbulletin.php in the importer folder.
Find:
'multiple' => $poll['multiple'],
Replace with:
'max_votes' => $poll['multiple'] ? 0 : 1,
You can also add in edit history if you want, which makes this importer have all the same features!