The character encoding when uploading to the server is not UTF-8. This can give problems when the model contains localized characters (e.g. in comments), as the XML parser used in the engine will complain by printing an error message. The GUI does not understand this message and the visible consequence is that no system appears in the simulator.
A fix has been checked into CVS. The fix is to always use UTF-8 when communicating with the server process.