Apple Calendar Email Alerts not working: "You must add your own card and email address in Contacts to be able to use mail alerts."
FINALLY!!! Solved! Does this solution work for you?
STEP 1: Go to Users and Groups in System Preferences
STEP 2: Click "Contact Card: Open..." button
STEP 3: Your Contacts app will open - It will open a contact card with your Username
STEP 4: Add your email to the contact card.
Presto! Emails alerts should work
Note: If in STEP 3 if there is no contact card with your Username, create one, add your email. Ensure you delete any duplicate contact cards with your Username.
Good Luck!