hashcash: 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/hashcash - from package: hashcash

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

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