Problems creating fillets on solid part

I`m trying to create some fillets on a tapered section.

The taper starts as an "H" section and changes to a "Rectangular" section over a 100mm length.

The transition takes place over 26 steps, the profile of each section (loft) is controlled by a design table (which doesn`t include the rads.).

This design table creates an "Cavity" part (see attachment), which is then "Cavity Cut" from a base block.

The external rads of the "H" are not a problem, but the internal ones !!!!!!!!!

No matter which form of Rad I try "Face Rad" or "Variable", its keeps coming up with "error messages".

I have even tried applying the rad after the cavity cut, but to no avail.

Can anyone suggest a way forward.

SolidworksParts And Features