I have recently modified a simulation on which I have been working for a few weeks and am getting good quality surface meshes as judged by the "A" and "E Ratio” scalar results, with very few narrow triangular elements. Most have an E Ratio of > 0.5. When I mesh the volume, it seems to mesh fine, per the "Vol" and "Vol Ratio" results. The entire volume is filled with a mesh. I have no triangulator or tetulator problems, and I have all the diagnostics turned on to show any problems in the log. The log reports none.

Feature-wise, the only difference between this simulation geometry and the previous simulation geometry (on which the solver ran fine) is the addition of an embedded face, which I turned into a two sided face that is a fixed-velocity inlet face. Both faces of the two sided face have the same BCs, the same air velocity, and the same flow direction per the X, Y, Z coordinate entries in the respective property panes. The geometry itself was made from a planar surface imported from Rhino as a STEP file that I revolved in Caedium to generate a solid. Then I imported the face to be embedded, Boolean subtracted it from the solid, and the geometry was all done. Most of the Rhino geometry elements were simply copied from those that worked well with the previous simulation.

However, after I attach vector arrows to the main seed face (there are four) and try to run the simulation, I immediately get the "FOAM FATAL ERROR: illegal cell label -1 in neighbor addressing for face...." message. This always happens at the very start, without the solver even appearing to start running. I also tried it with vector arrows attached to all four seed faces at the same time, and got the same error message.

I have read and re-read the Symscape page "How do I fix mesh and solver failures?" several times.
I have shaded all model faces. I have scrutinized the meshes and they seem okay, but I am not entirely sure I know how to evaluate the quality of volume meshes.
I initially set all faces to be walls, then went back and changed certain ones as needed to inlets, inlets/outlets, and outlets, so everything has some sort of BC set. After I could not get the solver to run, I went back and did this again.

I have the residual monitor up and ready to go. Sometimes - not always - it shows a residual trace going for a fraction of an iteration horizontally and then stopping.

Thanks very much in advance for your thoughts.