RFC problem: could not get functionname from XML requst (sic)

Question

I'm developing an interface that attempts to call a receiver RFC on an SAP 4.6c system.  It's a very small simple interface, and it's all working until it tries to call the RFC.  The error is
Exception caught by adapter framework: error while processing message to remote system:com.sap.aii.af.rfc.core.client.RfcClientException: could not get functionname from XML requst: com.sap.aii.af.rfc.RfcAdapterException: failed to read funtionname from XML document: missing namespace declara
I've created an RFC channel, which is green in the adapter monitoring.  The RFC imports without a problem, and appears in my interface mapping.  My mapping program converts to the RFC message type (as evidenced in sxmb_moni.  I have a receiver agreement referencing the interface mapping, which must be working as the mapping is called. 
Could anyone point me to what else I could check?  I saw a post about the same error message, where the respondent found something in the logs which helped them  Could you expand on what you found, and in which log please?  Any pointers as to which logging options I could switch on and check would be gratefully received.
Regards
Alan Graham

Answer 1

Thanks for the responses.
I set up a communications channel of type RFC, which is
showing green in the adapter monitor.  If I deliberately
break it, eg by changing the password, the adapter shows
as red in the monitor.  I assume therefore that the
adaptor settings are correct.
The XML going to the adapter looks correct AFAIK.  My problem is that I don't know enough about the requied XML to know if what I'm seeing in the logs is sufficient.  In SXMB_MONI, in the 'call adapter' section of a failed message, the outbound binding includes
<SAP:ToInterfaceNamespace>urn:sap-com:document:sap:rfc:functions</SAP:ToInterfaceNamespace>/code]
Also, the interface determination SOAP header, in the MAIN section includes
[code]<SAP:Receiver>
  <SAP:Party agency="" scheme="" />
  <SAP:Service>D04</SAP:Service>
  <SAP:Interface namespace="urn:sap-com:document:sap:rfc:functions">Z_MPU_3PSCE_FREIGHT_UPLOAD</SAP:Interface>
  </SAP:Receiver>
These are the correct values for the RFC name and the namespace, AFAIK.
I'm using an interface mapping (which uses and ABAP class as the mapping program) which references the interface of the RFC.  The logs tell me this works, ie, the class is called and the resulting XML appears in the payload of the response.
Alan