rxvt-xpm: 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/rxvt-xpm - from package: rxvt

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

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