Big problem: Site is live now, but I cannot do anything under "Customize"

I uploaded my website to a host server today and everything looks ok except everyone who looks at it said that my header is gone. So I logged in to Wordpress and I can see and edit all the pages, menus, everything, except if I go to anything under Appearance-Customize, then Wordpress shows the login page in the right pane and says, "Session expired. Please log in again. You will not move away from this page." I can login, but if I try to do anything under Appearance-customize, it logs me out again. What could be going on? The site is www.oakridgeoutlaws.org