I just downloaded it at work, and tried running it through the netfabb tool that Nicolinux linked to above, and it can't open the file.
Netfabb is a tool to repair invalid meshes. I made sure the mesh I made you was valid before I uploaded the file.
That being said, I ran it thorough Netfabb's cloud service (here) and it spat back an error. Once I removed the underscore from my file name, though, it worked fine. I've never used the download version of Netfabb, but perhaps that's the issue?
In any case, here's Netfabb's "fixed" version: https://www.dropbox.com/s/syyxxdz8oil32jl/msnew_fixed.stl?dl=0
Thanks so much for taking the time to help me! Hopefully I can figure out what I'm doing wrong. I haven't had a chance to try it out tonight, I had to go out searching for ugly Christmas sweaters for the kids for school tomorrow. Nothing like waiting until the last minute to tell me, but that's typical.