Hey @devang
It seems I’ve figured out the solution to the problem. I thought I could be clever and link up a single Boolean Toggle to all the different steps of the simulation, meaning I could just set the Boolean Toggle to “True” and then let the whole simulation run over night.
However, it seems that something gets tangled between the SnappyHexMesh and Solution when doing so. If I manually set the different steps to “True”, for example Solution after SnappyHexMesh is done refining, then I don’t get the error message and the simulation runs smoothly both in parallel and with a single CPU (still working in Rhino 6).
In a perfect world it could be nice to have the option to just switch on every step in one go, since SnappyHexMesh takes quite some time to finish, but I can easily live with this 
Thanks again for your suggestions. I will consider this topic answered and ready to be closed.
Have a great day!