Creating a sound object (e.g., dragging an MP3 into the Wisconsin demo so as to create a KMoviePlayer) causes TSoundBuffers to be created on-island. (In the Wisconsin demo example, these are initiated by #playLoop.) However, not every replicant will get these on-island sound buffers, and so the next available unique ID for the island will be off. The consequence is that some folks can get "no such object" errors.
I have verified that this happens (even with Wisconsin-jcg.100) when one replicant is headless (not rendering). I imagine (but have not confirmed) that it will also happen when different participants are in different locations (maybe even different positions in the same space?).