trees2prolog: 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/lib/fastdnaml/bin/trees2prolog - from package: fastdnaml

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

Error in other languages:
trees2prolog: bevel nie gevind nie
trees2prolog: comandă negăsită
trees2prolog: comando não encontrado
trees2prolog: commande introuvable
trees2prolog: command not found
trees2prolog: käsku ei ole
trees2prolog: không tìm thấy lệnh
trees2prolog: komanda nerasta
trees2prolog: Kommando nicht gefunden.
trees2prolog: kommandot finns inte
trees2prolog: komut yok
trees2prolog: nie znaleziono polecenia
trees2prolog: níor aimsíodh an t-ordú
trees2prolog: no se encontró la orden
trees2prolog: no s'ha trobat l'ordre
trees2prolog: opdracht niet gevonden
trees2prolog: parancs nem található
trees2prolog: perintah tidak ditemukan
trees2prolog: príkaz nenájdený
trees2prolog: příkaz nenalezen
trees2prolog: команда не найдена
trees2prolog: командата не е открита
trees2prolog: 命令找不到
trees2prolog: コマンドが見つかりません