wnckprop: 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/wnckprop - from package: libwnck-devel

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

On Debian possible default full paths are:

/usr/bin/wnckprop - from package: libwnck-3-dev

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

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