[Serusers] nat and multi domain problem

hi, I am new is this list and also in ser, sorry is the problem has a stupid solution. I am configuring a ser sip server with the following features: - Nat support with nathelper - Multidomain support with domain module. modparam("usrloc", "use_domain", 1) modparam("registrar", "use_domain", 1) All my uas are behind a nat box without sip support, therefore I fix_nated_contact in order to have a valid contact in location dadabase. The registration procedure works fine, and i can start a call with INVITE, the problem is when the caller send the ACK because in the request field get the contact in the user@ip_address:port way. The proxy is answering with "Not found" (because modparam("usrloc", "use_domain", 1), I guess.....), and from this point everything fail is the dialog. Any idea? Thanks very much for your help Antonio Higuera.