metacity-theme-viewer: 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/metacity-theme-viewer - from package: metacity-devel

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

On Debian possible default full paths are:

/usr/bin/metacity-theme-viewer - from package: metacity

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

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