Have a customer who is using a website to book an event. When she's done, it downloads the ICS file but when she clicks it, it just opens a dialog of the event in Outlook. Cannot save it or do anything with it.

Isn't there a way to add the event into the calendar? She does have two calendars (one is shared) and she wants to add it to the shared calendar... but I have also tried it on another account without shared calendar and it doesn't  work