gnome-xcf-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/gnome-xcf-thumbnailer - from package: gnome-xcf-thumbnailer

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

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