Hi Flippy,

I recreated the outer surface by copying the circle and the outline at the bottom and then using loft to connect the shapes. Then replaced your outer surface and joined to a new solid. It fillets now, at least here.

My guess is that the bottom outline was too fragmented. My original thought was to use a merge script to create a more continuous line, but it didn't work so I went ahead with the above solution.

I left the lines I used to create the loft so you can see.

ps. sometimes it seems like you have selected a whole loop to fillet, but there is a small unselected section that creates a problem. Scripts like this are handy for selecting loops fast (even if you have to deselect some parts after running the script):

script: /* Loop selection */ moi.geometryDatabase.selectLoop();

Select at least two consequent lines and it will find everything in the loop.