415 Unsupported Media Type - loading file

I'm pretty new to using SoapUI - I'm trying to run a WS that uploads a document 

Doc – a byte array containing the specified file

When I run the WS I get a message "The server cannot service the request because the media type is unsupported." or org.apache.xmlbeans.XmlException: error: Unexpected element: CDATA

any suggestions?  Thanks