Sorry for any confusion, after a little digging, here's what has happened:

Your "Annual Subscription" reminder was sent out on 26-Dec-2010, to the email address we have on file.
The email was rejected with status "550 5.5.1 Not Our Customer"--basically the message bounced.

Please check that the email address we have for you is current.
You can change your email address by clicking on "Settings" at the top of the screen, if need be.