Simulation is based on the jBPM runtime, it executes the business process in order to do simulation (replaces activities with simulated activities based on your simulation properties, etc). In case of models like in your example, we need to add more validation to tell users that some parts of the model (execution schemantics) are missing in order to properly run simulation.
In your case the outgoing sequence flows from the first XOR gateway do not have a conditional expression defined, so the simulation engine does not know how to proceed there and returns no results.
A quick fix for you is to add:
return true;
as the condition expression to the two outgoing sequence flows from the first gateway. This will allow the engine to return results.
We will add for the next release better validation and assistance so that users do not run into these types of issues. If you have any suggestions on that let us know.
HTH