Authentication question -- any idea why this would be?

I have an interesting message flow when my user agent registers
with Asterisk.
First it registers, then gets an unathorized. Then it registers again
with the digest authentication. Gets a second unauthorized. Then
it registers yet again and finally gets an ok.

Of the top of anybody’s head, any idea why it takes two unauthorized
messages?

THanks,
Mike

Post back a sip debug