fpack: 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/fpack - from package: libcfitsio-bin

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

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