xcal_cal: 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/xcal_cal - from package: xcal

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

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