asterisk users - Dec 2005 - appradius

I am trying to register my Asterisk to a Portabilling system. My asterisk 
registers with no problems, but when i try to send calls to portabilling I 
get the response:

Dec 14 15:23:31 WARNING[420]: chan_sip.c:727 retrans_pkt: Maximum retries 
exceed
ed on call 5f82691b2d83b8fc551f7097541a6c1e@XX.XX.XX.XX for seqno 104 
(Non-cri
tical Request)
    -- Executing SetCIDName("SIP/101-436a", "xxxxxxxx") in
new stack
    -- Executing Dial("SIP/101-436a", SIP/xxxxxxxx@XX.XX.XX.XX) in new
stack
    -- Called xxxxxxxx@XX.XX.XX.XX
Dec 14 15:23:51 NOTICE[420]: chan_sip.c:7177 handle_response: Failed to 
authenticate on INVITE to '"xxxxxxxx"
<sip:xxx@XX.XX.XX.XX>;tag=as1e4ccdd7'

Has anyone managed to successfully send calls from Asterisk to Porta?

Hello all.

Has anybody works with appradius? where can I find documentation?

Regards,

Jsalas