“OpenSCAD has some performance limitations when it comes to loading external STL files, so keep your polygon counts as low as you can. I like to use Meshlab’s “Quadric Edge Collapse Decimation” filter (under the “Remeshing, Simplification and Reconstruction” section) to reduce the number of faces in more complex models to get them to load in OpenSCAD.” – is the suggestion I’d take. In my experience OpenSCAD is amazingly bitchy about importing other models. If they are not absolutely positively perfect, it can’t tell inside from out, and will just botch the whole job. Try repairing the imported model in netfabb cloud before importing it, and if that doesn’t work, try meshlabs quadric edge collapse decimation as suggested on the page, and then again, repair…see if either of those helps. I find it’s prudent to have meshlab on your machine anyways, as well as netfabb for simple repairs.