Forgot to mention I am using Seam-Version: 1.1.0.GA
I think I may have finally figured out the answer (this has been bothering me for a few days, but of course I figure it out right after I post).
The application server reloaded my application, and I didn't refresh the page.
Therefore I am requesting an invalid conversation id.
Hopefully this helps somebody else.
I'm glad you worked out the problem. In general, the conversation model should work exactly the same via the remoting API as it does for a normal JSF action.