Thanks Leonid, everything is fine now, faxes are received properly!
Now I decided to look through other rtflog errors and warnings and found that most of them I cannot understand e.g.
08/05/2016 18:16:41.101 3804 1664 gc_h3r ERR1 sm.cpp:1198 ! 0 ! << genDefaultSigalStartParams Setting Max Subscription to 0.
08/05/2016 18:16:41.101 3804 1664 gc_h3r ERR1 sm.cpp:702 ! 0 ! << genSigalStartParams: MAx Subscription = 0: .
08/05/2016 18:16:42.249 3804 1664 gc_h3r ERR1 encoder.cpp:2367 ! 0 ! Encoder::sendSysMsg : encodeCallForward failed:No Call Forward data in DB.
08/05/2016 18:16:42.249 3804 1664 gc_h3r ERR1 board_device.cp:360 ! 0 ! << CallForward 
, sendSysMsg(MsgType_CallForward) failed!
08/05/2016 18:17:11.273 3804 172 sip_stack Error 000000AC ERROR - CALL - CallLegLock - Call 0x04D3DD58: CallLeg object was destructed
08/05/2016 18:16:43.231 3804 172 gc_h3r WARN sip_signaling.c:1364 ! 1 ! SipSignaling::releaseCall: BAD m_hsCall PARAM
Could you help me to correct them?