probme of voice in conference

i have probleme in agent session, when the customer answer, the agent can't listen the voice of customer and the same thing for the customer, i suposed that the probleme is in the conference because i have connect two agent in the same conference and i have the same probleme
for you information i work with vicidialnow 1.1 and the version of asterisk is 1.2
for you information i work with vicidialnow 1.1 and the version of asterisk is 1.2