ncal: 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/bin/ncal - from package: bsdmainutils

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

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