Asterisk 1.2.24 Got 200 OK on REGISTER that isn't a register


I’m using Asterisk 1.2.24 to receive incoming calls and outgoing call. Every thing is fine and working proper .

Some time my server showing this warning error :-

Jul 26 18:05:40 WARNING[2023]: chan_sip.c:9963 handle_response_register: Got 200 OK on REGISTER that isn’t a register

and that time i can not receive any call. When reload on localhost*CLI> command line its working and able to receive call, but warning error message come on every 5 to 10 minutes.

Plz tell me what is meaning of this msg and what wrong with my server ?

Does anyone know how to fix it?