I get the message that certain MP3 files cannot be foound but of course they are there, in the same place...the only problem I can see is that it is because there are spaces in the filenames and folder addresses - could this be the problem?
If so, could it be that the files were moved at some point after they were added to the project.
If this is not MP3 files in a project, then it might be necessary for you to run the program with administration rights. I do not think spaces in the file name or the folder would cause an issue unless there are some ascii characters in the name.