gdialog: 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/gdialog - from package: zenity

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

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