It was perfectly fine before the update and was never saved with any other program. The file has never been moved and my PC is fine. The only logical assumption I can come up with is that MED has not properly saved it. I've had damaged model files before in the past and they have never acted like this. They were damaged from being put onto cheap CD-RWs. This file hasn't even been on my hard drive for that long.

I saved it as an MDL5 and then as an MDL7 and that seems to have cleared up the problem for now. Thanks.