mountrw: 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:

/sbin/mountrw - from package: flashybrid

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

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