I downloaded the client for the first time three days ago (hi all, newb here!), and this morning I've been receiving the same message others have been: I need to download the latest patch. However, the patch on the website is dated July; I'm pretty sure the client I downloaded would have included this.
Given that we're all having similar problems, this sounds like a major server issue rather than user error. I'm just going to give it a few hours to see if it fixes itself.