SIP/2.0 404 Not Found

Hello

I use asterisk 1.2.
Have several sip accounts (working incomming connections).
And i have problem with another operator which says i have wrong configuration.
My sip.conf:
[MY_USERNAME]
secret = MY_PASSWORD
type = friend
username = MY_USERNAME
fromuser = MY_USERNAME
host = sip.halonet.pl
fromdomain = sip.halonet.pl
dialformat = ${EXTEN:1}
context = DID_trunk_1
insecure = very
allow = all
qualify=no

Dialplan is working fine (the same for all incomming connections).
When i try to call this number from other voip account i receive it’s busy.
My voip operator’s logs shows:

U 217.11.128.5:5060 -> MY_IP:5060
INVITE sip:MY_USERNAME@MY_IP SIP/2.0.
Record-Route: sip:MY_PHONE@217.11.128.5;ftag=4670C188-2553;lr=on.
Via: SIP/2.0/UDP 217.11.128.5;branch=0.
Via: SIP/2.0/UDP 217.11.128.50:5060;rport=57823.

U MY_IP:5060 -> 217.11.128.5:5060
SIP/2.0 404 Not Found.
Via: SIP/2.0/UDP 217.11.128.5;branch=0;received=217.11.128.5.
Via: SIP/2.0/UDP 217.11.128.50:5060;rport=57823.

What might be wrong ?

Thanx
Michal