I have a UA55ES7500 and I have the exact same problem, starting just a few days ago. I've tried everything on my end to fix it to no avail; from what I can work out, the problem must be with Samsung's servers. The two things I use my TV for the most are Plex and Skype and now neither will reinstall after the factory resets, making my TV next to useless.

I'm considering buying a Chromecast tomorrow to get me out of trouble, but if I have to go to that extent just to use my TV then it's doubtful I'll trust Samsung enough to ever shell out the sort of money they want for a TV again. The constant updates were bad enough, but the simple fact that the service has become so unreliable makes me think I'd be better off just getting a dumb TV in the future and using media players from other more-trustworthy companies to handle my media content.

Let me know if you find any way to get it working again because this is driving me mad at the moment.