ics-to-rss: 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/ics-to-rss - from package: vpim

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

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