Strange Normal Map problems.

I was finishing the Creating Weapons for a First Person Shooter course and the time came to bake the normals. I have baked normals before but I have never seen anything like this before. Basically, after baking around 80% of the textures, the bakes get corrupted with artifacts and if I try to bake a texture that I had previously baked, those get ruined as well. Jonathan suggested I try to copy the groups to a new .blend file but that doesn't really work.

I really want to solve this because I want to move on from this model and make my own guns but I don't want to leave this unfinished. Can someone please help? This is driving me nuts.

Here is the model https://drive.google.com/open?id=17GhMnF22Bhp57RZWn4HDJT1CHQRVrs8p

And here is the question thread https://cgcookie.com/questions/7003-what-causes-this