Thanks Phil and Momso.

The surfaces were joined and fillet failed. The Rhino file from Momso shows that fillet works fine when the edges are correct.

I made a new model (3dm file attached) and a close up of the 3D view shows a mis-match in the curved surface. It appears a portion of the outer surface extends into the cut-out area. This cutout was made by subtracting an extruded closed outline from the base solid.

Can this type of issue be repaired, or do I start over?

My solids are made from 2D lines created in Corel Draw saved as EPS. Out of habit, I find Corel Draw fast and easy for creating 2D.

I will try next to create my model entirely within MOI.

Ed