sendpeesmp6: 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/sendpeesmp6 - from package: thc-ipv6

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

Error in other languages:
sendpeesmp6: bevel nie gevind nie
sendpeesmp6: comandă negăsită
sendpeesmp6: comando não encontrado
sendpeesmp6: commande introuvable
sendpeesmp6: command not found
sendpeesmp6: käsku ei ole
sendpeesmp6: không tìm thấy lệnh
sendpeesmp6: komanda nerasta
sendpeesmp6: Kommando nicht gefunden.
sendpeesmp6: kommandot finns inte
sendpeesmp6: komut yok
sendpeesmp6: nie znaleziono polecenia
sendpeesmp6: níor aimsíodh an t-ordú
sendpeesmp6: no se encontró la orden
sendpeesmp6: no s'ha trobat l'ordre
sendpeesmp6: opdracht niet gevonden
sendpeesmp6: parancs nem található
sendpeesmp6: perintah tidak ditemukan
sendpeesmp6: príkaz nenájdený
sendpeesmp6: příkaz nenalezen
sendpeesmp6: команда не найдена
sendpeesmp6: командата не е открита
sendpeesmp6: 命令找不到
sendpeesmp6: コマンドが見つかりません