horde-writable-config: 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/horde-writable-config - from package: php-horde

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

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