A rather uninformative error is shown when opening a file via the 'Most Recent Files' menu item that has been deleted or moved. For me the latter was the case and since the path was rather long it was not immediately visually apparent that the path was outdated.
So when trying to open the mru item, Freemind shows a dialog with only: "An error occured on opening the file: <non-existing-file-path>". Only by inspecting the log and seeing the FileNotFoundException I realized what was going on. I had to do this via terminal by the way, as the menu item 'Help -> Log File Viewer' was still greyed out.</non-existing-file-path>
A more helpful error would be nice of course (and easy to implement I suppose), but a better route even, might be to stat the mru items and either remove them or mark them if they do not exist anymore.
Version details: Freemind 1.1.0beta2, Java 1.7.0_45, OSX 10.14.6.