Hi Tony, your object has a little separate slivery strip in it here:



Having that little slivery separate face there is going to get in the way of filleting. And also like Phiro writes above rotating it so the seams are not in the same spot can make it easier to fillet as well. It happens to avoid whatever glitch that the filleter was running into in this particular case.

I've attached a .3dm model file that should fillet ok for you.

- Michael