The xml returned by webservices invariably use namespaces. To access data contained in the xml you would need to declare namespace . To declare namespace you would select the process,right click the process select properties, click the advanced tab to create namespaces
For example the following is a example of namespace declared in workbench
where greg is the namespace prefix
I have included a simple process which makes a web service call to Amazon, using namespace I get data out of the response. The following is an example of using namespace in workbench
/process_data/xmlData/greg:Envelope/greg:Body/cole:ItemLookupResponse/cole:Items/cole:Item/cole:ItemAttributes Click here to get the PDF
Original article at http://eslifeline.wordpress.com/2009/02/06/using-namespace-in-workbench/.