Hi, when I try to open an existing project, I get a message that says it’s open on another machine.
Assuming that you’re certain it’s not open on another machine, you can just ignore this. If you’re not sure, you can make a copy of the project to work on.
What could have happened is that you made a copy or a zip of a project folder while it was open, in which case the lock went into effect for that copy/zip file, even though you afterward closed the original project folder.
I too have noticed it (and ignored) every time when using the “Backup Project to…” and saving as a zip file. Transferring this file to another PC and unzip and use you will get that message.
Lock file is backed up along with the rest of the project. So generally, can just be ignored.