I have recently had the same problem with my 40" Samsung LED TV, except my Smart Hub apps were actually working for a while. I bought the TV last summer, and until earlier this year I was able to download and use the apps available through Smart Hub. But, a couple of months ago I began to be unable to download new apps (though the existing ones worked fine), so I reached out to Samsung for help.
I spent three hours on internet chat with Samsung over three nights trying to resolve the download issue. Unfortunately, after the rep walked me through the first of many, many factory resets, ALL of the apps I had previously downloaded on the Smart Hub were gone, and I was unable to download any of them. Instead, got exactly the same grayed-out "Samsung Account" link and error messages you describe.
Over the course of those customer service chat sessions, the Samsung customer service reps and I reset Smart Hub and did a factory reset of the TV numerous times, in every conceivable sequence and combination of steps - we rebooted after unplugging the TV, rebooted after rebooting my internet router, rebooted the TV first and then Smart Hub, rebooted Smart Hub first and then the TV...and so on. None of those attempted fixes worked.
The only thing that we were unable to do was re-install the TV software (aka "firmware"). This seemed to be something we needed to do. When we ran the "Smart Hub Connection Test", we got an error message telling us we needed to update the TV software in order for apps to be available. I'm running version 2128 of the software. When I try to do the update through the TV from the Support menu, it tells me there are no new versions available. But, the Samsung customer service rep told me that there is, in fact, a newer version - 2207 for my TV - and directed me to the Samsung download center (here: www.samsung.com/us/support/downloads). There are instructions there for how to download the new firmware for your TV to a USB drive and install it directly from the USB to the TV. I tried to do this, but was unable to get my TV to recognize the firmware on the USB drive. BUT, I haven't ruled out that I did something wrong in that process, and that this is actually the problem that needs fixing.
Hope this helps. Please write back if you are able to fix your problem. It's driving me crazy.