This issue is caused by invalid mapping. In bw6, It is required to indicate that the mapping is for the child element. Mapping the root element will result in the above mentioned error.
This issue can easily be resolved by making the following change by using the xslt editor.
Open the Activity-->XSLT-source and changed the coercion as follows
From
<?xml version="1.0" encoding="UTF-8"?>
<!--START COERCIONS-->
<!-- $Response, type, m:Response -->
<!--END COERCIONS-->
to
<?xml version="1.0" encoding="UTF-8"?>
<!--START COERCIONS-->
<!-- $Response/*, type, m:Response -->
<!--END COERCIONS-->
Please note that $Response has "/*" added to it.
After making the above change, please click the button "parse" before saving the project.