Hi Denis,
Thank you for your reply.
I'd actually been editing the bundle-context.xml in the server-side of the plugin, rather than the ui code... I solved the problem by following the FAQ guidelines in the section: "Upgrade to use content negotiation based on the "Accept" header of the HTTP request in a backward compatible way". I was then able to upgrade the plugin successfully. I didn't realize it was to be applied in the server-side code before then.
Many thanks,
Warren