I think I've seen a similar thing happen in a couple of cases: backslashes are not valid characters for filenames, and the latest versions of Construct properly enforce that filenames are valid.
You should still be able to open the project in a previous release (see the releases page). Then you can rename any project files with invalid names to make them valid, save the project, and then it should open in the latest release.
I think we've also fixed some related issues in the latest beta release so the project may open fine there as well.