cisco-decrypt: 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/cisco-decrypt - from package: vpnc

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

On Debian possible default full paths are:

/usr/bin/cisco-decrypt - from package: vpnc

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

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