aptitude-curses: 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/aptitude-curses - from package: aptitude

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

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