If you see this message along with the error code ERR800, it means there was a problem accessing or creating your inbox. While this can usually be resolved by starting over, there are a couple of things you can try if that doesn't immediately work.
Restart your browser
Sometimes the old "turn it off and on again" solution actually works! Just quit your web browser, and then start it back up again. Once the browser has been restarted, go to mail.aol.com and enter your username and password.
Clear your browser's cache
Another way to fix this error message is to clear your browser's cache. This will wipe out all the little unwanted bits of info that have been stored in your browser, making it run better overall.