urxvtc: 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 CentOS possible default full paths are:

/usr/bin/urxvtc - from package: rxvt-unicode

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/urxvtc - from package: rxvt-unicode-256color
/usr/bin/urxvtc - from package: rxvt-unicode-lite
/usr/bin/urxvtc - from package: rxvt-unicode

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

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