Starting July 30th, you will no longer be able to log in to a Curse account that was not merged with a Twitch account. If you have not yet merged your Curse account with a Twitch account, please do so here! Otherwise, your account and its content will be inaccessible.
Right, now that I have your attention everyone, I do not have a fix for this error. This is because there is no fix, people, please stop spamming the Game Client support section with these titled posts, here is what you need to read now:
The Minecraft Servers are temporarily down! They will be back up soon!
Now you all know WHY they aren't up. This applies to everyone! Nobody can connect.