I also have the same problem - Newly installed Lightroom 6 Slideshow "Preview" and "Play' not working.
Can anybody help?
I am also have the same issue in Lightroom CC when adding music to a slideshow. I have some songs from itunes that load and play just fine. But the others come back with the error box "file format is bad". HELP!!
I see these queries remain unanswered.
I have the same problem with stand alone Lightroom 6.3.
I have set up a slideshow, but when I pressed the "Preview" key it merely states - "Preparing Slideshow - preparing preview for slide 2" as indicated in Stephen's query.
The slideshow contains 75 photographs & videos - I left it running all night and in the morning the screen reflected - "preparing preview for slide 13". i.e.prepared 13 slides in about 8 hours!!
Please HELP - very frustrating!
same issue with the last LR Classic CC 2017