In EMPro this error comes up fairly often. All FEM padding is set to zero since it's a waveguide structure which has been shelled with the only open ports being the waveguides, and the face of the waveguide is the outer face of the geometry. Sometimes the error goes away by simply closing EMPro and re-starting it. Sometimes the error goes away by changing the shell thickness. Sometimes the error goes away by changing the curvature of one of the objects inside the structure, such as by changing the radius of a blended edge. But often none of these work-arounds fix the problem and you're left with a structure that EMPro refuses to simulate. Does anyone have other work-arounds that they've used that worked for getting rid of this error?