Error in transformation steps

Hi

I have a scenario where i need to send to source messages to ont target message ,I am tring to do using BPM.

I have used steps

1)recive step to recive the file(I am giving here 1 msg type from two)

2)Transformation step to transform two sources to 1 target

3)Send file to pick the file.

I am not doing any configuration for the transformation step...

Error in bpm work flow technical details at mapping error..

*****com/sap/xi/tf/_eadress_mm_com.sap.aii.utilxi.misc.

api.BaseRuntimeExceptionRuntimeException in

Message-Mapping transformatio~******

I have tested messape mapping & interface mapping they where no errors..

Can any please help me how to work with transformation or can any one please send sample weblogs which explains transformation step in detail...

Thanks

sriram