I am having that problem too, this is the 2nd time in two days that it has happened to me. Unfortunately the only way to fix it is to uninstall and then reinstall the game. As I am writing this I am waiting for the install to finish. I did research to see if there was another way to fix this problem. There are troubleshooting guides for this specific issue, don't bother none of that works. At least for me they didn't. I followed all the directions in those trouble shooting guides to a T and nothing. And reading the forums this actually is a common problem for alot of players. There is no rhyme or reason, not when the game works perfectly one day and then all of a sudden this error appears for some players not all. Just know nothing is wrong with your computer, nothing is wrong with your internet connections, just like nothing is wrong with mine. This is an ongoing issue from Square Enix, it's their problem that they need to fix and don't let the devs or tech support tell you different. TLDR: Uninstall then Re install.