mrxvt-full: 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-full - from package: mrxvt

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

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