Flow Simulation issue - Graphics error or other problem?

Hello

Im trying to run a flow simulation on this model for my college project but I am having issues and I am not sure what it could be.

The results slow black areas on the cut plots and flow trajectories will show black lines in the same areas.




Have i set up the simulation wrong or is it just a graphics error.

The model is quite complex (assembly).

Thanks in advance

SolidworksFlow Simulation