At what point do you see the error message about some mandatory configuration could not be loaded? That's normally a database access error so maybe the mail platform is having trouble finding your mailbox on the mailbox server. It may be a temporary glitch so try again in 30 minutes.
Post back with the details if it's still happening. What you can do first is clear the browser cache and cookies just to make sure there's no corrupt cookie or page load hanging around. Or try a different browser.
