For some reason, the Insert event to a "primary" calendar, didn't do the job. Instead, i wrote the following code, which allowed me to write the event.
var list = service.CalendarList.List().Execute().Items;
service.Events.Insert(e, list[0].Id).Execute();
This is my solution for this problem, I also agree with Craig here that the API is not well organized. (saying this after working with the amazing API of maps).