Interconnection between an Asterisk and a PABX

Hello,

I want to connect my Asterisk (phone number : 3XX) with my SIEMENS PABX v6 SIP (phone number : 2XX and 1XX).
On my Asterisk, I create a SIP trunk : when an Asterisk phone compose a phone number like 101, I use my trunk.

There is a problem “486 Busy Here” and I have this error message when a phone of my PABX SIEMENS composed a phone number of my Asterisk :

asterisk1*CLI>
– Executing AbsoluteTimeout(“SIP/5060-08b01e78”, “15”) in new stack
– Set Absolute Timeout to 15
– Executing Congestion(“SIP/5060-08b01e78”, “”) in new stack
== Spawn extension (from-sip-external, 405, 2) exited non-zero on ‘SIP/5060-08b01e78’
– Executing AbsoluteTimeout(“SIP/5060-08b01e78”, “15”) in new stack
– Set Absolute Timeout to 15
– Executing Congestion(“SIP/5060-08b01e78”, “”) in new stack
== Spawn extension (from-sip-external, h, 2) exited non-zero on ‘SIP/5060-08b01e78’

Do you have already this error?