jcal: command not found

Have You tried accessing the binary with the full path?

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/jcal - from package: jcal

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