lwt-toplevel: 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/lwt-toplevel - from package: liblwt-ocaml-dev

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

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