xsec-xklient: 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 Debian possible default full paths are:

/usr/bin/xsec-xklient - from package: xml-security-c-utils

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

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