wnck-urgency-monitor: 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/wnck-urgency-monitor - from package: libwnck

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

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