MRIConvert: 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/MRIConvert - from package: mriconvert

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

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