IAX not registering

hi,

I have a strange problem. IAX clients can not register with my asterisk server. If I restart the server (core restart now) and try within 2-3 second client get registered. But if I disconnect the client and try again it doesnt get registered. From tcpdump trace in server end I can see iax requests are coming from client and hitting the right port, but if I set iax debugging on (iax2 set debug on) i see nothing. I can see Asterisk is listening to port 4569 from netstat,

netstat --listen | grep iax udp 13056 0 *:iax *:*

Below is my iax configuration:

[general]
bindport = 4569
bindaddr = 0.0.0.0
;bandwidth = low
disallow = all
allow = g729,g723.1
trunkmtu = 1240
trunkfreq = 20
trunktimestamps = yes
iaxthreadcount = 30
iaxmaxthreadcount = 100
minregexpire = 60
maxregexpire = 2000
;autokill = yes
codecpriority = caller
requirecalltoken = no

[anat]
callerid=Anat
username=anat
secret=anat
type=friend
host=dynamic
context=test
disallow=all
allow=ulaw
allow=alaw
allow=gsm

Im totally clueless on what the issue is. Any help will be highly appreciated.

Thanks in advanced!