Why do I receive calendar invitations that don't work ever since I changed my UCSBnetID?

This happens because the event creator invited you using your old Connect address, <oldnetid>@ucsb.edu. If they have used the old address to invite you in the past, it still exists in their Contacts and was available to select in the "Add: Guests" field. The invitation you receive is non-functioning because you are logged into Connect as <newnetid>@ucsb.edu. For more infomation, please see Changing My UCSBnetID.