Clear your browser's Cache and Cookies
Your browser stores a lot of information about websites, you, and (for example) your ability to log into websites in its Cache and Cookies. If these bits of code get messed up or out of date, this can result in all kinds of problems. So a good first step if you're having trouble with a website is to clear your browser's cache and cookies and then try again.
Please note: If you have Duo set to "remember" you, this is a cookie, so after you clear your cache and cookies you'll have to go through the two-factor process the next time you log into Carleton sites.