Synch. RFC call error - No Sender Found

Hi,

once execute the synchronous RFC call from BPM, rfc response message returns as following;

<SAP:Code area="RCVR_DETERMINATION">MESSAGE_INCOMPLETE</SAP:Code>

<SAP:Stack>Message is incomplete. No Sender found</SAP:Stack>

i've tried adding header mappings at receiver aggreement for bpm's name as sender service and target sap system name as receiver service. Same error.

Any help is greatly appreciated. Thanks