Project suddenly won't open

I have a Cubase 7.5 project that has worked for some time, but suddenly no longer opens. The thing is, if I copy the project folder to any other drive, it works perfectly. At the same time, on the drive where the project does not open, all other projects WILL open. So, it seems there’s no problem with the drive, and the project does not seem to be corrupted since an exact copy opens from any other location. I made no changes to my system of which I am aware - the project was just working one day, and the next day it was not.

Has anyone ever experienced this before? Thanks.