Can not make a call

Hi guys, i need help, i built asterisk with a2billing successfully, i created account number of a2billing and after that i registered successfully on soft phone but when i want to make a call
i can not call, i get this error:

== Using SIP RTP CoS mark 5
– Executing [[email protected]:1] Answer(“SIP/8872948899-00000019”, “”) in new stack
== Spawn extension (a2billing, 123453992318674, 2) exited non-zero on ‘SIP/8872948899-00000019’

My Voip system was built asterisk 1.6, freepbx 2.7 and a2billing stable 2.9, Please help me