asterisk users - Jan 2009 - line disconnected after 20 seconds no reply to our critical packet

Dear all,

I have from time to time problems with disconnect after exact 20 seconds.

I have these problems from time to time in LAN after using PickUP() with 1.2
I have these problems from time to time in WAN when the internet connection is 
not reliable with 1.4

Is there any way to fix it?

best regards
Thomas


[Jan 10 13:18:36] WARNING[4102] chan_sip.c: Maximum retries exceeded on 
transmission 5e608496-e9a1cd54 at 123.123.123.123 for seqno 102 (C
ritical Response)
[Jan 10 13:18:36] WARNING[4102] chan_sip.c: Hanging up call 
5e608496-e9a1cd54 at 80.80.173.155 - no reply to our critical packet.