change_pw: 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/lib/mailman/bin/change_pw - from package: mailman

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

On Debian possible default full paths are:

/usr/lib/mailman/bin/change_pw - from package: mailman

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

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