absolutely imperative that you use GroupCalendar 4.0. – prior versions cannot synch with version 4.0 and all [official] events that are posted by the guild leader are posted using version 4.0. it is almost guaranteed that if you are not signed up for a raid in GroupCalendar, that you will not be going on that raid.
(note: you can ask the event organizer (Ironhelm in the case of this Saturday) to sign you up if you cannot install GroupCalendar addon; however, that should not be your normal approach.)
