grxvt: 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/grxvt - from package: rxvt-ml

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

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