If you are not receiving updates to events on your calendar, it may be because you copied an event from another calendar. When you copy events, any changes made by the owner of the event will not appear on your calendar.
To have the event appear on your calendar and to receive updates regarding changes, contact the owner of the calendar and ask them to invite you through the Tell a Friend link on the event. When you accept a calendar invitation from the owner of an event, you automatically receive email notifications any time the calendar owner edits or updates the event.
If the owner of the calendar previously invited you to an event, they need to delete you from their list of Screen Names and email addresses on the Tell a Friend screen, then re-enter your Screen Name or email address in order to re-send the invitation to you