Hi Tony - what radius of a fillet are you trying to create?

There are several different issues on your particular model here that will make it difficult to fillet.

One is that your object is quite thin and so only a fillet of a very small radius would even be possible to fit on it.

But also another thing that will probably make it difficult is that your model seems to be made up of multiple fragmented pieces instead of bigger smooth surfaces, for example see these vertical edges here:




The front surface of your model there is not just one big surface but is instead made up of multiple surfaces, and filleting will tend to have difficulty handling situations where you have multiple surface fragments like that where the surfaces are not totally smooth to one another but are somewhat close to being smooth like meeting each other in a shallow 5 or 10 degree angle or something like that.

When 2 surfaces touch each other totally smoothly then it's ok since fillets that are constructed will touch each other naturally where they meet up.

When surfaces are sharp where they meet, then fillets do not meet up naturally and instead they need to have a lot more processing done with fillets getting extended and intersected with one another and then corner patches put in to then connect up the trimmed back pieces. All this stuff is much more difficult to handle when things are meeting at a shallow angle, things like the corner patches become little tiny slivery things and it's also more difficult for the intersector to do a good job when things are at such a shallow angle.

So anyway, in order to fillet this you instead want the front and back parts of your model to be made up of bigger surfaces instead of fragmented into smaller pieces.

It looks like your generator curve that's flat on the x/y plane is made up of a lot of little different sub-segments. If you select it and then run Edit > Separate on it to break it into its individual segments you will see that a lot of small pieces are then individually selectable. That segmentation in the generator curve is going to cause segmentation in the surfaces generated from it, so you want to get that generator curve to be better constructed before building more stuff off of it. Probably the easiest way to tune it up is to use the Rebuild command on it:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

So anyway probably your model as it currently stands is going to be quite difficult to fillet - I would recommend reconstructing it to have a cleaner construction with a smaller number of broader surfaces rather than having it made up of so many different fragments.

- Michael