More info on this.
It could be related to non-english characters in folder names. If you have issues with repro, let me know and I can send you a zipped tree of empty folders to test.
I can also repro runtime error 53 when I do a directory browse in the main screen, then use double click to navigate in the tree. When I double click on the parent folder that contains these non-english char sub-folders, I get the error and frodoplayer closes.