mkvsyvf: 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/mkvsyvf - from package: vftool

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

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