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.
I have a UA46EH5300 Samsung Smart TV and it used to work great.
A few days ago my Plex app started failing. So I uninstalled it, hoping that a reinstall would help.
But now, none of my applications are installing.
When I select "Download" in the app store, it simply goes from "Downloading" immediately to "Installing" to "Download" again without actually installing the app.
The problem is, its now doing this on many other apps as well. Which to me seems to indicate that there is some file lock or something on the download, so it thinks it already has the install file, but then it fails.
I called Samsung Support, and they were next to useless because I'm probably out of warrantee.
I have reset the smart hub about 7 times already, hoping that it would clear the installed apps, but that seems to do very little "resetting" other than clearing the meta data of what is installed. It doesnt actually clear any installed apps.

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