Hi ,
Take the payload from test tab of your message mapping and process the message from rwb/integration engine/test. -->You will get to know whether is it due to namespace issue or any other.
By the way at what stage message got failed.At mapping level or before/after that?
You can simply track it ,by looking into trace.Hit on trace button in sxmb_moni and dig for reason for which message got failed.
Regards
Venkat