Yahoo! Mail

Your login session has expired.

For your security, your Yahoo! Mail session expires a maximum of twenty-four hours after you have logged in. If you have chosen in your Yahoo! User Information (found be visiting "My Account" next to the Yahoo! Mail logo at the top of this page) to be prompted for a password more frequently than every day, your session will expire after the specified amount of time.
If you do not accept the cookies set on login or your computer is not configured to accept cookies, your session will expire almost immediately. We use cookies (small pieces of site information) to assist us in user authentication and in saving configuration information. Cookies are required for Yahoo! Mail.

If you see this message immediately after logging in, you should check the following:

Check to see that your computer system time is accurate. Cookies are time sensitive and may not work if your computer date is incorrect by a large amount.
Make sure that your browser is configured to accept cookies or that you agree to accept cookies during the login process.
Turn off any third party programs or control panels that automatically reject cookies.