[Serusers] phone + pstn with ser and cisco gateway

[Miquel]

I have a big problem with a gateway (cisco) and ser. 
Phone to phone with sip it's ok and when i do phone to pstn the
packets arrive to gateway but the line is busy and the message (when i
made a capture with ethereal ) is -BAD REQUEST Invalid IP.

I don't know what i have to configure. I think the ser.cfg is well
because the packets arrive to the gateway a it reposes.

My quenstions:
- I have to register the gateway
- What i have to do

Thanks 
- - 
Miquel