sdif2ad: 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/sdif2ad - from package: csound-utils

You may install the required package with command apt-get install {package}
Error in other languages:
sdif2ad: bevel nie gevind nie
sdif2ad: comandă negăsită
sdif2ad: comando não encontrado
sdif2ad: commande introuvable
sdif2ad: command not found
sdif2ad: käsku ei ole
sdif2ad: không tìm thấy lệnh
sdif2ad: komanda nerasta
sdif2ad: Kommando nicht gefunden.
sdif2ad: kommandot finns inte
sdif2ad: komut yok
sdif2ad: nie znaleziono polecenia
sdif2ad: níor aimsíodh an t-ordú
sdif2ad: no se encontró la orden
sdif2ad: no s'ha trobat l'ordre
sdif2ad: opdracht niet gevonden
sdif2ad: parancs nem található
sdif2ad: perintah tidak ditemukan
sdif2ad: príkaz nenájdený
sdif2ad: příkaz nenalezen
sdif2ad: команда не найдена
sdif2ad: командата не е открита
sdif2ad: 命令找不到
sdif2ad: コマンドが見つかりません