IAX2 Max retries exceeded Error

Dear Friends,

I am using two asterisk boxes in my Call Center which are communicating each other by IAX. I have Digium TE412P card installed on first box. Calls land here and these are immediately forwarded to the second server using IAX. AGI and Queues and all sort of things are on the second server. Now my problem is after a few hours running nicely an error starts filling up on the CLI screen of the second server. The error message is : "WARNING[31641] chan_iax2.c: Max retries exceeded to host 192.168.1.33 on IAX2/192.168.1.33:4569-10180 (type = 6, subclass = 2, ts=40002, seqno=11)", where 192.168.1.33 is the first server. Once this error start coming, the calls are not landing on the agent's extension. But still calls are answered by the second server and welcome message is played, they are asked to make language selection etc and after that only the call is going blank. This indicates that there is no comunication problem between the servers. Once this problem starts the only way to resolve is to reboot the second server, after which it works fine again for another few hours or some times 1 or 2 days. Also I tried asterisk 1.4.21.2 and asterisk 1.2.30 which gave me the same error. But asterisk 1.2.25 didnt give me this error. It has another error.

Could anybody please help in resolving this IAX error. Its very seriuos because we are losing business.

Thanks & Regards
Shanavaz.