simpleproxy: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/simpleproxy - from package: simpleproxy

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