I've encountered the same problem twice this weekend. Best I can figure, the system's no longer accepting "Unknown" as a last name. It might be by intention, but that seems strange indeed. We'd miss out on a lot of mothers if the LNAB must be known before you can create a profile. Another possibility is that we've used up all the numbers available for "Unknown", not unlike the Y2K problem that never really was. My best guess is that there was a strange problem with the last "Unknown" profile entered - file corruption or something, and the counter's messed up.