Can't Knit Surfaces

From the SW help files:

Use the Knit Surface tool to combine two or more faces and surfaces into one.

Note the following about knit surfaces:

• Edges of the surfaces must be adjacent and not overlapping.

• Surfaces do not need to be on the same plane.

• Select the entire surface body, or select one or more adjacent surface bodies.

• Knit surfaces absorb the surface bodies you used to create them.

• Create a solid body when the knit surfaces form a closed volume, or leave as a surface body.

I beleive you're violating the first rule.  The outer surfaces of your box overlap the rib surfaces.  Try it with a two simple test surfaces, it still doesn't work.  Also, some of the edges of your ribs extend beyond the box.

I'm not sure how to get all of the features you want into a single surface.

I dont think that can be done because knitting surfaces look for edges to knit at least that is how I understand it.

UPDATE:

I may indeed be wrong I am looking at some other issues that could be the problem

Stuart,

I don't think there is anything wrong with your import or part. I might have misunderstood you or what you are doing, but the knit command can only perform a Knit where two or more surface body edges are in close proximity to one another. It looks like you're trying to knit your interior ribs with the interior wall - that is not possible with the knit or trim mutual command because the interior wall is continuous and does not topologically break where the rib/s are located. What you simply have to do is thicken the overall box and then thicken each of the ribs to merge it into the box. (see attached.)