try running these commands, and then trying the restore again:
afterwards, you'll want to run
zmprov mcf -zimbraAccountExtraObjectClass posixAccount
zmprov mcf -zimbraAccountExtraObjectClass sambaSamAccount
Those commands enable and disable the extra account attributes needed for samba/posix. If the account was created before you installed the samba addons, then the restore is bailing because uidNumber is a required atrribute that was not included in your backup. After restoring, browse to the users tab in zimbra, set and save the posix and samba attributes.
zmprov mcf +zimbraAccountExtraObjectClass posixAccount
zmprov mcf +zimbraAccountExtraObjectClass sambaSamAccount
Hope this helps.