Hello
im having “call ended” when incoming call…
from debugging iv got : Got SIP response 420 bad extension back from …
can any one solve it to me?? 
Not on that information.
Also this is not the right forum for support questions, like that. It is intended for discujssions.
From the SIP RFC:
[quote]21.4.15 420 Bad Extension
The server did not understand the protocol extension specified in a
Proxy-Require (Section 20.29) or Require (Section 20.32) header
field. The server MUST include a list of the unsupported extensions
in an Unsupported header field in the response. UAC processing of
this response is described in Section 8.1.3.5.
[/quote]
You will need a SIP trace to see what it was rejecting, or you could just try turning off the bells and whistles until it is happy.