nwns: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/mafft/bin/nwns - from package: mafft

You may install the required package with command apt-get install {package}

Error in other languages:
nwns: bevel nie gevind nie
nwns: comandă negăsită
nwns: comando não encontrado
nwns: commande introuvable
nwns: command not found
nwns: käsku ei ole
nwns: không tìm thấy lệnh
nwns: komanda nerasta
nwns: Kommando nicht gefunden.
nwns: kommandot finns inte
nwns: komut yok
nwns: nie znaleziono polecenia
nwns: níor aimsíodh an t-ordú
nwns: no se encontró la orden
nwns: no s'ha trobat l'ordre
nwns: opdracht niet gevonden
nwns: parancs nem található
nwns: perintah tidak ditemukan
nwns: príkaz nenájdený
nwns: příkaz nenalezen
nwns: команда не найдена
nwns: командата не е открита
nwns: 命令找不到
nwns: コマンドが見つかりません