Problem with multipartrelated content type


Were having issues with trading networks and the ariba on ramp accepting a cXML message in our production environment.
The message is multipart mime message including some well formed xml and a binary attachment.

The problem occurs when our vendor uses the multipart/related content type in the headers for their post. The error we get in trading networks is

2004-01-31 14:59:34.0 No cXML document received from sender.
Payload ID :

                      From         :   () 
                      Sender       :   () 
                      To           :   () 

                      Additional Log Data 

                      DocumentType :  
                      SubType      :  
                      MessageSender : 

If we use the multipart/mixed content type, the problem does not occur and trading networks processes the message ok.
Also, in our test environment, both content types work just fine.

Asking our vendor to change their headers is a rather long drawn out process and so I am keen on finding a fix for why this is happening only in our production environment.

Does anyone have any experience with this problem? Any ideas on what we can do to fix it ?
Any help is greatly appreciated

multipart/related is a generic content-type which is used by C1market connect, aribaonramp, ebXML etc… Pls make sure that only one of the above packages mentioned is installed on a single IS.