task_manager.pl: 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 Debian possible default full paths are:

/usr/lib/sympa/bin/task_manager.pl - from package: sympa

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

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