I received an upgrade LR to 6.6.1 today (end July 2016), did so, and went to use Slideshow. I received a message that the video card is not supported. Eventually I found on the Adobe sight that this was a known issue (from April 2016) and that I had to install an older drive for the AMD Radeon card 6600M and 6700M series. I did so, from the relevant AMD support link, restarted everything and same issue, Slideshow not working as video card not supported. It worked fine in the previous version LR 6.x. And I'm surprised given an automatic update today with a known issue from three months ago, so, anything that actually works?