The most common reason for a message of this type is because the "missing" 7 files are no longer in the exact location they were when the project was last saved.
So, have you moved those files, even possibly allocated a different drive letter to the drive where they are stored?
Or, potentially even more problematic, have you deleted those files from your computer? If so, unless you have a backup of them somewhere the project can never be successfully reopened.
If none of these ideas are applicable to your situation, can you please post a screenshot of the actual error message you see, or at least the FULL wording of it, please?