vpnc: 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/vpnc - from package: vpnc-consoleuser
/usr/sbin/vpnc - from package: vpnc

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

On Debian possible default full paths are:

/usr/sbin/vpnc - from package: vpnc

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

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