debconf-set-selections: 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/debconf-set-selections - from package: debconf

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

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