This method can be used from the board level device, or from channel device what is involved in the call. If you use GCTGT_GCLIB_CHAN, the board handle must be specified. For in-call IMs you should use GCTGT_GCLIB_CRN as a target, and provide a real CRN for that call. Also, please check if
virtBoards[0].E_SIP_MESSAGE_Access = ENUM_Enabled;
is set for gc_Start