Having had a similar experience a few months ago, I would first try clearing your cache and try a different browser.
If/when that doesn't work, call DCL as soon as you can tomorrow. There was some kind of a "setting" on our reservation that the phone rep was able to fix in under a minute that magically made the website work after a couple of days of frustration.
Why Disney has "settings" that involve the website not functioning for paid in full guests is a question I can't answer.
Similar problems. I removed cookies from the site then logged out and logged back in. The past few days I have had to log out then log back in for the site to work.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!