Embed Vaadin Portlet in Liferay Theme?

I’ve been trying to embed a vaadin portlet into a Liferay theme with no luck. This is using Liferay 6.1.1CE and Vaadin 6.8 . Even the simplest portlet, for instance one that just displays a Label, results in a “Communication Error”. Is this impossible to do, or am I just messing up (or both)? If not it isn’t a big deal, I can just re-implement as jsps + AlloyUI, but it would be nice to know what my options are.