aediff: 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/aediff - from package: aegis

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

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