Confbridge on openwrt


I have installed asterisk on my OpenWRT Router. The standart package does not include confbridge. So I copyed manualy the “” into the modules. It would be loaded successfully but it doesn’t work.
Here are the message from asterisk:

  == Using UDPTL CoS mark 5
  == Using SIP RTP CoS mark 5
    -- Executing [20@sebastian:1] Goto("SIP/2001-00000014", "konferenz,s,1") in new stack
    -- Goto (konferenz,s,1)
    -- Executing [s@konferenz:1] Answer("SIP/2001-00000014", "") in new stack
    -- Executing [s@konferenz:2] ConfBridge("SIP/2001-00000014", "0815,M") in new stack
[Dec  5 07:47:56] ERROR[22800]: app_confbridge.c:455 join_conference_bridge: Conference bridge '0815' could not be created.
  == Spawn extension (konferenz, s, 2) exited non-zero on 'SIP/2001-00000014'

What went wrong ? Ist there any other modules needed to run confbridge ?