n_categories: 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/fastdnaml/bin/n_categories - from package: fastdnaml

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

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