Unable to create solid from surfaces

Hi all,

I am currently having difficulties making a smart solid from 3 different surfaces that I created using the 'Loft' tool.

The issue I think occurs from the original shapes, being that of a 'pringle crisp' shape the arcs along the shape go off in different directions from each other and that of the other shape lofting between.

This caused me some issue originally when trying to loft between the curves, though eventually I manage to create the surfaces.

My issue now is that no matter what I try, I just can't seem to get the surfaces to convert to 'smart surfaces' and therefore can't create a 'smart sold'.

If someone could have a look at the file attached for me and hopefully find solution, that would be great!

I am hoping it is something simple that I have just missed.

Kind Regards

David

Concrete Surround.dgn