MKVSYall: 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/MKVSYall - from package: vftool

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

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