Please help! I've exported loads of slideshows before, but suddenly it won't work. I think the only change is that I upgraded my Macbook to the newest version (10.12.2) and I updated Lightroom CC to the 2015.8 version. Slideshow plays fine in preview or play mode through lightroom, but when I export it, I only get a black screen. Searched the forum and nothing seems to solve my problem. My "Graphics Processor" is disabled/unchecked. Tried with and without music. Tried with only 2 images. Tried landscape only images. Tried with all RAW and then all JPEG. Tried all 4 size options for the export. Nothing is working!
Maybe try deleting (or temporarily renaming) the preferences file and see if the problem persists. Information about how to find the prefs file is here: Preference file and other file locations | Lightroom CC and 6
Let us know if that helps.