I started with an imported surface to which I made some modifications. I sewed the piece to have only a surface body and from there I can't thicken it, an error message is displayed "Has not shifted the surface or the face could not be removed."
(Note: the imported surface cannot be thickened, the error message is "could not thicken the surface").
Is this a mistake from the imported surface or is there another way to thicken a surface?
I'm thinking of something else, you try to thicken to 0.5mm but isn't there a radius in your surface that is much smaller and therefore prevents thickening?
If this is the case, first delete these "face deleted" spokes in connection mode!
If the fthomas solution (offset surface) works, even with a small or very small value, try to offset the surface several times until you get the offset value of 0.5mm
Then, remove all the polygon bodies between the two offset surfaces needed and use polygon features (as boundary surface) to create the "sides" and finally recreate a volume.