There are two common reasons. The first is detailed at the following link.
What this limitation means is the web sites have to make their sites and video compatible with these Smart TVs.
Some folk were expecting the browser and such to be on par with a Windows PC. It is not.
Basically, I can use my smarthub just fine with netflix, other apps, etc. However when I go to, lets say CBS.com, and try to watch a television show, the show starts, then freezes. This happens to more than just that one website. It's pretty much anytime I want to watch a tv show from a website. Any ideas? Samsung online chat said to reset the smarthub, but I read this will reset everything, and since I have no issues with smarthub itself, or getting to the internet, I am afraid to do this - that it may cause me more work to resolve. TV model is UN55D7000. Thank you.