sass-convert: 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/sass-convert - from package: ruby-sass

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

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