Cracks can only be created on Quadratic Tetrahedral elements. Did you set the Mesh to Quadratic?
Automatically meshed Semi-Elliptical cracks must remain in the solid body. The minor radius is 10 mm and the largest contour radius is 10 mm so the part must be at least 20 mm thick for the mesher to work. I don't think your geometry is more than 20 mm thick is it? You also need a base mesh that has many elements covering that 20 mm depth.
See my reply in this discussion: