This has happened two or three times: While trying to open a project in V15 Evo, I recieve an error saying the file is already in use, or has an error in it. This is not resolved even after a restart. The only way I have found to resolve this is to delete the whole project file, and replace it with the one from my backup, and then it opens fine (any work I had done since that last backup is of course lost and must be redone).