Restoring a backup fails

I am having some difficulty restoring a backup. Here is the output I am seeing:

Extracting TAR file of home directory …
… done

Setting ownership of home directory …
… done

Re-creating mail and FTP users …
… done

Re-creating mail aliases …
… done

Moving inbox mail files …

Restore failed : Missing file to open at mailboxes::/usr/share/webmin/mailboxes/folders-lib.pl line 1434

Does anyone have any idea what the missing file would be? Or why I would be getting this error?

Thanks.

So looking in the folders-lib.pl file, line 1434 is two lines after this comment:

# For Maildir to mbox moves, just append files

So I am thinking that I have not setup my new server correctly, to use maildir instead of mbox. Is my thinking correct?