Xdialog-gtk1: 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 CentOS possible default full paths are:

/usr/bin/Xdialog-gtk1 - from package: xdialog

You may install the required package with command yum install {package}

Error in other languages:
Xdialog-gtk1: bevel nie gevind nie
Xdialog-gtk1: comandă negăsită
Xdialog-gtk1: comando não encontrado
Xdialog-gtk1: commande introuvable
Xdialog-gtk1: command not found
Xdialog-gtk1: käsku ei ole
Xdialog-gtk1: không tìm thấy lệnh
Xdialog-gtk1: komanda nerasta
Xdialog-gtk1: Kommando nicht gefunden.
Xdialog-gtk1: kommandot finns inte
Xdialog-gtk1: komut yok
Xdialog-gtk1: nie znaleziono polecenia
Xdialog-gtk1: níor aimsíodh an t-ordú
Xdialog-gtk1: no se encontró la orden
Xdialog-gtk1: no s'ha trobat l'ordre
Xdialog-gtk1: opdracht niet gevonden
Xdialog-gtk1: parancs nem található
Xdialog-gtk1: perintah tidak ditemukan
Xdialog-gtk1: príkaz nenájdený
Xdialog-gtk1: příkaz nenalezen
Xdialog-gtk1: команда не найдена
Xdialog-gtk1: командата не е открита
Xdialog-gtk1: 命令找不到
Xdialog-gtk1: コマンドが見つかりません