virtfs-proxy-helper: 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/virtfs-proxy-helper - from package: qemu-system-common

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

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