Newbe Question about Radii/Fillet

I have a part I wish to draw. It looks like a rectangle 30" x 6" on
the front plane but the upper and lower bars are radiused to 400" in
the top plane.
I started the part but inserting a plane parallel but offset 6" to the
top plane. I drew a radius and constrained it to origin and defined
the cord of the radius to be 30". I copied the radius to the new
plane I inserted. I then drew the vertical bars to connect the end
points.
I now have a rectangle with square corners when viewed parallel to the
front plane but a single radiused line when viewed parallel to the top
plane.
I then drew a circle to represent the cross section and sweep the
radius along the 3D path I created.
I've gone back to the sketch and tried to fillet the corners of the
sketch but am given an error reading "Cannot fillet curves that are
not co-planar."
After sweeping the curves, I've tried using the Solid fillet command
and got an error reading " the radius of the fillet is too large to
fit the surrounding geometry. It may be too large because it cannot
fit within a tightly curving face near a selected edge or it would
inappropriately eliminate an adjacent face. Try adjusting the input
geometry and radius values or try using the "Face fillet" option."
This is a 1/2" dia bar swept along the curve that I had intended to
use a 2" radius in the corners when formed.
Can someone point me to what I've overlooked to be able to fillet or
radius this part?

R. Wink