celtdec051: 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/celtdec051 - from package: celt051

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

Error in other languages:
celtdec051: bevel nie gevind nie
celtdec051: comandă negăsită
celtdec051: comando não encontrado
celtdec051: commande introuvable
celtdec051: command not found
celtdec051: käsku ei ole
celtdec051: không tìm thấy lệnh
celtdec051: komanda nerasta
celtdec051: Kommando nicht gefunden.
celtdec051: kommandot finns inte
celtdec051: komut yok
celtdec051: nie znaleziono polecenia
celtdec051: níor aimsíodh an t-ordú
celtdec051: no se encontró la orden
celtdec051: no s'ha trobat l'ordre
celtdec051: opdracht niet gevonden
celtdec051: parancs nem található
celtdec051: perintah tidak ditemukan
celtdec051: príkaz nenájdený
celtdec051: příkaz nenalezen
celtdec051: команда не найдена
celtdec051: командата не е открита
celtdec051: 命令找不到
celtdec051: コマンドが見つかりません