asterisk users - Mar 2005 - Windows Messenger and 481 error

I just upgraded to CVS-HEAD and when I am using Windows Messenger 5.0
or Potrait I get the following error :


Registered SIP '2000' at 203.76.169.170 port 3912 expires 120
    -- Saved useragent "RTC/1.2.4949" for peer 2000
    -- Got SIP response 481 "Call Leg/Transaction Does Not Exist" back
from 203.76.109.170


 i can't dial any number eve though I am registered.Any suggestions to
get out of this .

Thanks.

Ehsanul Karim