You've got a whole load of redundancy in that path!

To fix it, open a command prompt and rename the "Beethoven, Ludwig Van" directory to a single character

That should make the path shorter so that you can rename the file to reduce its overall length.

I suggest:

D:\_MP3\CLASSICAL\Composers A-B\Beethoven, Ludwig Van\Sonatas for Piano\Piano Sonata in C Minor\05 - Op 111 1st Mvt.mp3

And use tags rather than file names on your MP3's