Exporting lattice structure as STL

We've created a lattice structure using the Engineering - Lattice tool by first extruding a solid and then replacing it with a lattice. Our lattice is a formula-driven gyroid with Replace body with lattice checked. When we export the part as a STL-file and try to import it in to our CAD software it fails.

When checking the geometry in meshlab using Filters - Quality, Measures and Computation - Compute geometric measures we get :

"Mesh is not watertight, no information on volume, barycenter and inertia tensor"

Any ideas on how to proceed?

PTC CREO 8.0.4.0