Permission denied problem in Freenas + Transmission
Solution 1:
Go to your FreeNAS web interface and browse to Advanced > Command.
From here, execute the following command:
chown -R transmission /nmt/4-1000gb/tv/Lost
(are you sure it isn't /mnt/ instead of /nmt/?)
You mentioned that your Transmission user name is TorrentUser, so if the above doesn't work you could also try this:
chown -R TorrentUser /nmt/4-1000gb/tv/Lost