This appears to be a bug in the 4.2.1 codebase as the parsing is expecting a CDATA section in the XML. It should have been using a Text element instead as the parsing code cannot force the text to be CDATA.
Is there any reason why you are still using the 4.2.1 codebase on the client? If so then you will need to edit the serialisation and replace all references to CDATASection with Text.
No problem - I have updated to 4.3 on the client and it works fine.
Just reporting it so that you would be aware of the issue.