What version of Premiere Elements and on what computer operating system is it running? Nevertheless....
I suspect that what you are seeing has nothing to do with file protection/copyright.
And, I believe it has everything to do with a media-project disconnect because
1. you moved, deleted, or renamed the file/folder that was imported into the project after the project was saved closed.
2. you stored your source media on an external hard drive and the drive letter of that drive has changed to something other than what it was when you first imported media from it into the project.
Where is the missing file on the hard drive at this time?
Are you getting "Where is the file _____?" message when you re-open the project? If so, use those message(s) to make the media-project reconnects one by one. But, you need to tell the project via those messages where you know the missing file to exist.
Please review, consider, supply more details, and let us know the outcome. If any questions or need clarification, please do not hesitate to ask.
I think you’re right and I think I’ve solved the problem. Thanks for the reply.
Thanks for the follow up with the great news that you think that the problem has been solved. Well done.
Please do not hesitate to ask if questions or need clarification on your Premiere Elements workflows.