We developed a multi-node application that uses RMI and a master/slave setup to coordinate animations on 4 Pi nodes. The whole thing is written in Java.
It works fine running locally on a Pi. It also works fine running with master and slave running on any combination of Mac and Windows. It does not, however work with one Pi node.
The Pi can communicate with a RMI'd object residing on other nodes. However, communication with RMI'd objects residing on the Pi times out.
The Pi is not running a firewall. It is on the same subnet as the other nodes. It is reachable, and can be pinged. We have tried using different port numbers for the RMI service point. We have also executed the program as root, and using a permissions file (not required to run correctly on Mac or Windows...)