Hi,
I had a similar problem and i found that the response wasn't a SOAP response because i got a response error.
I catched the problem marking the flag Do not use SOAP envelope in the SOAP receiver. Later i did a XSL transformation in the request wrapping the XML with the SOAP envelope. Finally, i can get the exact response that the webservice was returning from sxmb_moni and i found an unexpected format for that response.
Hope this helps.
Regards,