Have you looked in The Plugins Index ? Here's an STL import/export tool http://forums.sketchucation.com/viewtopic.php?p=209946#p209946 There are also other threads about STL files and 3d-printing in general etc. This took 2 seconds [in mm]Housing.zip

@dave r said: It looks to me as if you have a couple of internal faces. You could probably just delete the top edges that were highlighted by the plugin and it would be fine. that assumes the top faces on either side of those lines are co-planar. If not, orbit inside the model and delete the faces or delete a face on top so you can see the internal faces and delete them, the trace along one edge (not those highlighted edges, though) and heal the missing face. Dave! Thank you so much! lawll i did try the deleting edges beforehand, but that also deleted a huge chunk of other stuff. I never thought to delete the actual inner face! haha, thanks again