Seems to be a problem in Simplify, but Flashprint, Cura and Makerbot print works at the moment. (at least for me). Gonna try to fix it.
Edit: was a few versions behind in Cura can slice it in 2.4.
Edit 2: Seems to be a weird error in the mesh but fixed it using netfabb. Will ask the boss to upload the repaired model when he can.
This fix will make it slicable in Simplify3D
If you want to fix it yourself load the model into netfabb (you can get a 30 day free trial).
Click the "red cross" on top of the UI. This will take you to a new workspace.
In the bottom left click "Automatic repair" and choose the "extended repair" option.
When its done click the "Apply repair" in the bottom left. Choose the option you want. (I used "remove old part")
You will jump back to the normal workspace.
Right click the model and export as stl.
Hopefully it works for you as well.