Hi Corn, hi Victor,
so I guess I got something now

First of all, the AttributeExtension 'status' =128 just means that the DN is out of service. From the T-Library SDK 7.2 C Developer's Guide:
0x80: DN is out of service. -------->128 decimal

0xC0: DN is undergoing maintenance.
0x90: Device associated with DN is locked out.
0x88: DN is vacant.
From the full log I have got from Corn what I can see is:
[list]
[li]T-server reads the DNs configured,[b] correct[/b];[/li]
[li]T-server doesn't register any of them, [b]correct[/b] since Corn has selected "On-demand" registration in CME;[/li]
[li]as soon as T-server gets the RequestRegisterAdress from the client, it forwards to the Avaya switch, [b]correct[/b];[/li]
[li][i]without [/i]waiting the answer from the switch, it replies to the client with a EventRegistered (status=outofservice) and an EventDnOutOfservice: a bit strange, but I've already seen this behaviour somewhere else with the new 7.2 T-server: it somehow processes the request just internally... [/li]
[li]and then the surprise!

(Corn, you didn't attach that part of the log in your very first post):
1. T-server gets the answer from the switch, a successful registration, [b]good[/b], it means the DN exists and it's on service on it;
2. T-server sends an [b]EventDnBackInService[/b] (status=0, ok&no activity on it) to the client! From now on the DN is
in service and can manage the client requests. [/li]
[/list]
So, for me everything works fine..! Corn, probably your client is not able to manage the EventDnBackInService?