jp2-thumbnailer: 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/jp2-thumbnailer - from package: openjpeg-tools

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

Error in other languages:
jp2-thumbnailer: bevel nie gevind nie
jp2-thumbnailer: comandă negăsită
jp2-thumbnailer: comando não encontrado
jp2-thumbnailer: commande introuvable
jp2-thumbnailer: command not found
jp2-thumbnailer: käsku ei ole
jp2-thumbnailer: không tìm thấy lệnh
jp2-thumbnailer: komanda nerasta
jp2-thumbnailer: Kommando nicht gefunden.
jp2-thumbnailer: kommandot finns inte
jp2-thumbnailer: komut yok
jp2-thumbnailer: nie znaleziono polecenia
jp2-thumbnailer: níor aimsíodh an t-ordú
jp2-thumbnailer: no se encontró la orden
jp2-thumbnailer: no s'ha trobat l'ordre
jp2-thumbnailer: opdracht niet gevonden
jp2-thumbnailer: parancs nem található
jp2-thumbnailer: perintah tidak ditemukan
jp2-thumbnailer: príkaz nenájdený
jp2-thumbnailer: příkaz nenalezen
jp2-thumbnailer: команда не найдена
jp2-thumbnailer: командата не е открита
jp2-thumbnailer: 命令找不到
jp2-thumbnailer: コマンドが見つかりません