/
is not allowed in folder names as of r317. However this still shouldn't prevent the project from opening.
In r308.2 I can create a subfolder named open/close
in the project bar, save, and open the project in r317; it opens successfully and automatically renames the folder to openclose
. So this kind of error shouldn't happen. Can you share your project file or file an issue so I can make sure other similar projects open successfully?