fasttreeMP: 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/fasttreeMP - from package: fasttree

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

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