reviewers can't download papers (not the same as previous)

I haven't been able to find any real documentation, so I've done my best to get the system up and running, and many aspects work fine. The main problem is this: when reviewers log in to get the reviews, they get an access denied error (unless they are made conference administrators or are given edit content node permissions -- both of which mean the reviews are no longer blind). There doesn't appear to be any way to grant download permission to reviewers without also giving them access to everything else. As it's configured, there isn't any other way to access the submission (e.g. the plain text version isn't available under 'my reviews' -- only the link to the attached file), short of having the editor mail the attachment out by hand (and once you're doing that, what's the point of having a system in place in Drupal?)

(Incidentally, the email to reviewers does not provide a link to the file to be reviewed either).

Any help would be greatly appreciated.