Asterisknow 3.0 configuration problem


I installed AsteriskNOW 2.0 and at the end of conventional installation I could make internal call using 3XC phone, now I have made ​​the same installation but using AsteriskNOW 3.0, and I noticed that the call success and as soon as I pick it cut. (we say that the signal passes but the voice packet does not pass).
Should I install something of special for the communication passes normaly? If YES what and how?
Ps: I am a new be in Asterisk

thank you