mrxvt-mini: 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/mrxvt-mini - from package: mrxvt-mini

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

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