Hi Jakob, We've never gotten this model to run, I believe it has to do with the 3-state control formulation instead of the 4-state one I used in my previous work (see SIGGRAPH 2012). The walking simulations using 4 states weren't as good as the 3-state ones using this model, that's why we dropped it...

Hope you've had some luck on this issue. The main thing I can think of is to make sure you preserve enough digits when you write them out to file. You could also try the same thing on a simple simulation using a standard OpenSim muscle model, just to see if the issue is indeed in the SimpleMuscle cl...