In your model, you tried to use one brake model for both the left and right wheels. In doing so, you rigidly connected the left and wheels together so they cannot rotate independently. That creates a problem for the initialization (and it isn't physically correct either).
The model runs fine if you delete the mechanical connection between the left and right wheels on the front and rear axles. I adjusted the model and attached it to this answer (Vehicle_DrCycle_Detailed_v1.slx). I suggest you add in independent brakes for all four wheels.
--Steve
