nspluginviewer: 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/nspluginviewer - from package: kdebase

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

On Debian possible default full paths are:

/usr/bin/nspluginviewer - from package: konqueror-nsplugins

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

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