This server could not verify that you are authorized to access the requested web page. Either you supplied the wrong credentials (e.g., the password does not go with the e-mail address supplied), or your browser doesn't understand how to supply the credentials required, or a firewall, proxy, or other network device is preventing the transmission of your credentials.
Recall, your e-mail address is your user id. The case of the letters in both the user id and the password matter.
If this problem persists, your best course of action is to re-assign your password to your user id. You must obey the instructions and reply to the password confirmation e-mail before your new password will work.
Older firewalls, web proxies, and other devices which allow more than one computer to share a single IP address may not correctly transmit requests for user ids and passwords. (They do not support HTTP version 1.1 authentication.) Never being prompted for a user id and password is a sign of this problem. Without these credentials you will not be given access to the pages for new and revised manuscript submission. Old versions of the Linux masquerading code (problem noted with Linux 2.2.12) are known to have this problem.
Accounts do expire after a long period of inactivity.