ics_diff: 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

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/ics_diff - from package: python-vobject

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