stag-flatten: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/stag-flatten - from package: libdata-stag-perl

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