I'm trying to place a call between two SIPp instances over FreeSWITCH. Before the connection is set up completeley FS sends a BYE to the caller. In the logs is see the hangup cause is "UNALLOCATED". That happens only if there is a pause after sending the ACK.

Hangup sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060 [CS_EXECUTE] [UNALLOCATED]
2008-04-17 14:53:46 [DEBUG] switch_channel.c:1293 switch_channel_perform_hangup() Kill sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060 [KILL]
2008-04-17 14:53:46 [DEBUG] switch_core_session.c:619 switch_core_session_signal_state_change() Kill sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060 [BREAK]
2008-04-17 14:53:46 [DEBUG] switch_core_state_machine.c:405 switch_core_session_run() sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060 Running State Change CS_HANGUP
2008-04-17 14:53:46 [DEBUG] switch_core_state_machine.c:431 switch_core_session_run() (sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060) Calling Handler for State HANGUP
2008-04-17 14:53:46 [DEBUG] mod_sofia.c:258 sofia_on_hangup() Channel sofia/freeswitch.mocon.esk.fraunhofer.de/bob@freeswitch.mocon.esk.fraunhofer.de:5060 hanging up, cause: UNALLOCATED