Sourcing integration: message "ID: Content is not allowed in prolog."

Dear all,

I'm integrating SAP Sourcing wave 9 on demand with SAP ECC 6 EhP 6 and I get an error when transferring sourcing awards to ECC quotations: "Message from webpage: ID: Content is not allowed in prolog.". There is no error shown in the PI, and when I test the mapping directly in the PI I also get no error.

I found out that this error message generally means that there are some characters preceding the xml opening tags

<?xml version="1.0" encoding="UTF-8" ?>

<ns0:MT_Award xmlns:ns0="http://sap.com/xi/ESourcing/SRMJS">

but I found none.

My questions are:

1. does this error message result from the PI or from Sourcing?
2. how can I track down the error as nothing is shown in the PI?

Can anybody give any hints?

Thanks,

Karsten