ivdowngrade: 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/ivdowngrade - from package: inventor-clients

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

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