add_ds.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/bin/add_ds.pl - from package: flowscan

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

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