vboxputty: 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/sbin/vboxputty - from package: isdn4k-utils-vboxgetty

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

On Debian possible default full paths are:

/usr/sbin/vboxputty - from package: isdnvboxserver

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

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