Ansys Employee

The cells are OK but the mesh isn't. One of the requirements is aspect ratio and another is growth rate.  I suspect you've got a change in flow (ie a gradient) in the left-right direction and it's then causing the solver to fail. 

Have a look at porous jump (it may not be suitable here) and also some of the meshing videos/tutorials to see what's been done there. As an aside, for multiphase I tend to avoid poly-hexcore and just use a poly mesh to avoid the jump in cell size in the free stream. That's fine for aero models where they can refine wakes ahead of time but not so good for multiphase models where we generally aren't as sure where stuff is going to go.