Thanks so much for the reply!

I just checked my Flash and Java, all up to date there. Does FFXIV use IE or my default browser? I was under the impression that it used IE, but I updated Opera just to be sure. Writing this post also gave me the idea that maybe Opera isn't supported, so I set the default browser to Chrome, but that didn't work either. I also checked my Windows Features as you suggested. Good call with that, it seems .NET 3 wasn't fully enabled. Unfortunately, enabling it brought no change, and the launcher client still gives me the same HTTP error.