ml-ulex: 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/ml-ulex - from package: ml-lpt
/usr/lib/smlnj/bin/ml-ulex - from package: ml-lpt

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

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