ncgen3: 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 CentOS possible default full paths are:

/usr/bin/ncgen3 - from package: netcdf

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ncgen3 - from package: netcdf-bin

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

Error in other languages:
ncgen3: bevel nie gevind nie
ncgen3: comandă negăsită
ncgen3: comando não encontrado
ncgen3: commande introuvable
ncgen3: command not found
ncgen3: käsku ei ole
ncgen3: không tìm thấy lệnh
ncgen3: komanda nerasta
ncgen3: Kommando nicht gefunden.
ncgen3: kommandot finns inte
ncgen3: komut yok
ncgen3: nie znaleziono polecenia
ncgen3: níor aimsíodh an t-ordú
ncgen3: no se encontró la orden
ncgen3: no s'ha trobat l'ordre
ncgen3: opdracht niet gevonden
ncgen3: parancs nem található
ncgen3: perintah tidak ditemukan
ncgen3: príkaz nenájdený
ncgen3: příkaz nenalezen
ncgen3: команда не найдена
ncgen3: командата не е открита
ncgen3: 命令找不到
ncgen3: コマンドが見つかりません