Hi,
I've the same problem.
I've create the log with only the problem (the log is in attach).
One gateway (messagenet.it) and two internal account (1002 and 1008).
My dialplan:
<include>
<extension name="messagenet.it">
    <condition field="destination_number" expression="^(5300000)$">
      <action application="set" data="domain_name=$${domain}"/>
      <action application="transfer" data="1008 XML default"/>
    </condition>
</extension>
</include>

My Sip Profile:
<include>
<gateway name="messagenet.it">
    <param name="username" value="5300000"/>
    <param name="realm" value="sip.messagenet.it"/>
    <param name="from-domain" value="sip.messagenet.it"/>
    <param name="password" value="password"/>
    <param name="register" value="true"/>
    <param name="retry-seconds" value="30"/>
</gateway>
</include>

My freeswith is runnig on Windows Server 2003 with 2 NIC (1 interna 192.168.0.15 and 1 external 10.0.3.6 (212.001.001.001))

For privacy I've change my IP and my phone number.

--
Alby