fssrgen: 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
/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/fssrgen - from package: fsharp

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