sessreg: 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/sessreg - from package: xorg-x11-server-utils

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

On Debian possible default full paths are:

/usr/bin/sessreg - from package: x11-xserver-utils

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

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