Registration error when using stun

Hi, im working in a company with a project where im supposed to implement
stun support to their sip-client. The problem i have is that the
sip-client when using stun (stun4j) cannot register to the sip sever. I
retrieve the correct ip and port that my computer has on the outside of
the NAT. And the ip:port are in the via header of the registration. When i
use ethereal there are no sip messages sent out to the sip server. I'll be
very gratefull for some help on this issue.

best regards,

Charbel Haddad