paprefs: 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
/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/paprefs - from package: paprefs

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