krxvt: 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/krxvt - from package: rxvt-ml

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

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