WindowsMail Error Message

When I open Windows Live Mail, I get the following error message:

We have noted some unusual activity in your account. Your action is needed to make sure no one else is using your account.

To continue, click OK. (done)

It looks like someone else might be using your account.

To help you-and only you-get back into XXXXXX, we need to verify that it is yours.

(The email account specified in the message is an old email address no longer in use. How do I get rid of this error message?)