RFC and Abs interfaces in MM

Hi everyone,

My scenario is HTTP-XI-RFC. I have done the request, response mapping (MM and IM). I need to send the errors from the rfc response to another BPM which handles errors. How do I map the RFC response to the abstract interface of BPM in interface mapping? when I select RFC in source interface and the abstract interface from BPM in target interface in IM, I couldnt select the message mapping between their message types. What is the solution for this?? Also, when I click on read interfaces, i see request in the bottom for selecting msg mapping...

plz suggest..