gallery1-to-slideshow: 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/gallery1-to-slideshow - from package: dvd-slideshow

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

Error in other languages:
gallery1-to-slideshow: bevel nie gevind nie
gallery1-to-slideshow: comandă negăsită
gallery1-to-slideshow: comando não encontrado
gallery1-to-slideshow: commande introuvable
gallery1-to-slideshow: command not found
gallery1-to-slideshow: käsku ei ole
gallery1-to-slideshow: không tìm thấy lệnh
gallery1-to-slideshow: komanda nerasta
gallery1-to-slideshow: Kommando nicht gefunden.
gallery1-to-slideshow: kommandot finns inte
gallery1-to-slideshow: komut yok
gallery1-to-slideshow: nie znaleziono polecenia
gallery1-to-slideshow: níor aimsíodh an t-ordú
gallery1-to-slideshow: no se encontró la orden
gallery1-to-slideshow: no s'ha trobat l'ordre
gallery1-to-slideshow: opdracht niet gevonden
gallery1-to-slideshow: parancs nem található
gallery1-to-slideshow: perintah tidak ditemukan
gallery1-to-slideshow: príkaz nenájdený
gallery1-to-slideshow: příkaz nenalezen
gallery1-to-slideshow: команда не найдена
gallery1-to-slideshow: командата не е открита
gallery1-to-slideshow: 命令找不到
gallery1-to-slideshow: コマンドが見つかりません