Load-balance: call hang up after a while when transfetrred

I have two asterisk servers with an outbound campaign
The Load balance works well when the call goes to an agent on the same server. But when the call is transferred to an agent to the second server (from the first) the agent begin speaking, but after a while (15-30 seconds) the call stops.
It may be à g729 codec issue!
vicidial 2.0.4.1 RC 5
asterisk 1.30.2
ubuntu Hoary
an idea?
The Load balance works well when the call goes to an agent on the same server. But when the call is transferred to an agent to the second server (from the first) the agent begin speaking, but after a while (15-30 seconds) the call stops.
It may be à g729 codec issue!
vicidial 2.0.4.1 RC 5
asterisk 1.30.2
ubuntu Hoary
an idea?