icalfilter: 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/icalfilter - from package: ical2html

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

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