Weird issue SIP REGISTER (401 Unauthorized)

when i look at my firewall logs i keep seeing this weird registration issue.

2nd event
02/21/2013 07:41:26.432 Debug VOIP SIP Response (asterisk)x.x.x.x, 5060, X1, 55925, X0 SIP REGISTER (401 Unauthorized) (111

1st event
02/21/2013 07:41:26.400 Debug VOIP SIP Request (phone)x.x.x.x, 55925, X0 (asterisk) x.x.x.x, 5060, X1 SIP REGISTER (111@x.x.x.x)

any ideas why i am getting this error?

forgot to mention that it doesnt prevent me from making and receiving calls.

It is probably normal. The 401 response tells the requestor how to go about authorising the request.