If, from the simulator, you save a non-empty trace and immediately open it again, it does not want to load the trace. Example: create a model of one automaton with one location and a transition from that location to itself. From the simulator take one transition, save the trace and open the trace again. You get an IO Exception.
Changed description to "Saving does not work", as loading a trace file generated by verifyta does work.
Confirmed.
A fix has been checked into CVS.