[Freeswitch-dev] Sofia Reg Failure every 5 minutes

Hi, Sorry for posting this to the dev list, but i got no response from users. I see the following message every 5 mins or so :- 2009-03-29 19:07:42 [ERR] sofia_reg.c:1263 sofia_reg_handle_sip_r_register() faktortel Registration Failed with status Operation has no matching challenge [904]. failure #1 followed by this :- 2009-03-29 19:07:42 [WARNING] sofia_reg.c:310 sofia_reg_check_gateway() faktortel Failed Registration, setting retry to 60 seconds. 2009-03-29 19:08:43 [NOTICE] sofia_reg.c:268 sofia_reg_check_gateway() Registering faktortel 1 minute after. The gateway seems to work fine, any hints as to what would be causing it? thanks dave