VIM workflow receiver function module problem

hello,

there is VIM workflow WS00275264

event linkage for WS00275264 is BUS2081-POSTED has been activated

the SWEL event trace shows a problem

in the Trace Data section, RFC status says "Message Type is unknown"

infact another workflow WS53800006 linked to the same event starts properly and this one doesnt start

there seems to be problem with receiver function module /OPT/BL_PO_BLK_RECEIVER

I tried changing it to the normal receiver FM SWW_WI_CREATE_VIA_EVENT_IBF (just to check) but then it gives error Event BUS2081 POSTED for task WS00275264 not defined as start/end event

Does this call for an SAP message ?

how to trace the problem for this error saying Message Type unknown

thanks

bhakti