I downloaded the game today and completed the beginning tutorial as a guest while my patcher was still downloading the game. After that i went to register an account and after i did it told me to restart the game. Upon doing so I would always run in to the "failed to connect to server press OK to retry or Cancel to exit" issue and this is how i fixed it.

I logged into my account on the site and sent the registration email and then confirmed it via the link. After that you can stop the downloader and exit it completely. Simply reopen rift and log on to your proper account and then you download should resume and you should be able to play again.

Hope this helps!