plasmawallpaperviewer: 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/plasmawallpaperviewer - from package: kdebase-workspace

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

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