A path variable usually shouldn't point to the file itself, it should point to the directory that contains the file.
I would guess that torrent flux is the same. So when it is trying to find the "unzip" binary, in your case it is looking for "/usr/bin/unzip/unzip" which doesn't exist.
That being said, i haven't used torrentflux in many years, if I recall correctly, it hasn't been maintained for a long time, and may well be full of security bugs. Based on the dates in the tarball, they are all aroudn 2008.
Perhaps try using "/usr/bin" in the torrentflux configuration.