G729 codec problems

hi all
i have asterisk running on Athlon 64 AMD processor, iam trying to make calls from SIP@G729(from quintum) through asterisk to ooh323@g729(to softswitch) but it does not work… i can hear the called party but i cant be heared and sometimes i got echo when i speak, is it a processor problem? ot just codec? actually iam confused because some people told me to buy the license but as u see iam in passthrough mode so iam not doing any transcoden (G729 to G729) by the way asterisk works good at (ooh323@g729 to ooh323@g729) and it is ok sometimes at (SIP@g711 to ooh323@g711)
if u help me i will appreciate