Hi Jim, so the problem seems to be that some of the surfaces of that little pocket piece were not close enough to each other to be joined into a shared joined edge which is needed to do an edge fillet.

The problem is in these edges here:



If you zoom in a bit and hide the faces, leaving only edges to be displayed, you can see that there are actually 2 separate edges in those areas instead of one common joined edge between the surfaces there:



So in other words, it's kind of like a gap or hole in the model in that spot, the edges are not joined into a single unified edge right there.

So probably that will need to be repaired, I'll take a bit more of a look in a minute here.

- Michael