I have a simular issue, not quite the same but related.
I want to send myself an email alert, and I get the "You must add your own card and email address in Contacts to be able to use mail alerts"
I then press the open cantact button, but then what ? I see no way to add my address from my own card.
Sorted it now I had to "Make this my card"
I'm not sure if the ealier reply was clear enough. The idea was that you need to make your card in the Adrress Book, your own as follows:
1. Go to your card (your name, etc) and highlight it (click on your name which will turn the font from black to blue)
2. Go to "Card" from the menu up on top and from the drop-down-menu click on "Make This My Card" - that will make that card, or whichever you had previously highlighted, YOUR OWN and iCal will use that to send any/all invites out via email.
I should mention that to undo the above, click on a different card and follow the same steps. That will remove the "Make This My Card" off the current and apply it to the new one.
Hope it helps. It fixed the issue in iCal immediately.