registration: 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/cmtk/bin/registration - from package: cmtk

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

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