guake-prefs: 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 CentOS possible default full paths are:

/usr/bin/guake-prefs - from package: guake

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/guake-prefs - from package: guake

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

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