Hi,
 
 Trying to do the following:
    pstn->SER->asterisk (call forward)->SER->Pstn
 The far end rings but when you answer the call, I get an error in Asterisk: "Got SIP response 481 "Invalid CSeq Number" back from XXX.XX.XX.XX (SER).
 
 I have tried the same using two SER machines with the same result, but if I change the scenery to  pstn->SER->asterisk (call forward) -> asterisk-> Pstn, it works fine!
 
 What could be wrong here? Does anybody implemented the scenery explained above? Could anybody give me a clue?
 
Thanks a lot.
 
 Regards,
  Victor.