kpac_dhcp_helper: 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/kpac_dhcp_helper - from package: kdelibs3

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

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