It's OK, I got the name of the marvel-agent plugin wrong anyway ;). I probably should have figured that out from the context of the output.
I'm guessing you only have the single node then, and that it's the same node that you are pointing Kibana at. Do you see the marvel indices in your cluster? Assuming you're using the default indices:
Also, check the time on your server and make sure it lines up with the time in your browser. If it's more than 10 minutes apart, you'll see the no data error.