[Asterisk-Users] username/auth name mismatch

[sasa]

Hi, I have a asterisk/voip newbie and I am sorry if my quetion is banal.
I used in my private LAN, Express Talk on Windows XP and Asterisk latest 
version on Fedora Core 4 , with this configuration in Express Talk

Lines menu:
Setting for Line: Default Line Settings
Full 'friendly' Display Name: port
SIP Numeber: 200
Server: 10.0.0.112
Password: mypassword

In menu Network:
Local SIP Port to Listen on: 5070
Local RTP ports: 8000

My sip.conf:

[200]
type=friend
callerid=port
username=200
secret=mypassword
host=dinamic
context=internal

My extensions.conf:

[internal]
exten => 200,1,Dial(SIP/200,20)

..but in Asterixk log file I have:
Registration from '<sip:200 at 10.0.0.112>' failed for '10.0.0.230 - 
Username/auth name mismatch

and on Express Talk I have:
Register attempt for sip:200 at 10.0.0.112 failed
404 Not found

..where:
10.0.0.112 -> asterisk ip address
10.0.0.230 --> express talk ip address

..where is my error ?
thanks.
Salvatore.