The likely reason for this is the end of support for old encryption methods. You and everyone else here should probably read this news article on the community site.

Given that this occurred today, it is very likely this is the reason for the error.

http://www.playonline.com/ff11us/polnews/news26736.shtml

Some older versions of Windows will not be able to use the newer encryption at all, and thus will not be able to play anymore without updating to a newer version of windows.