I'd say don't bother to correct the error, just click "No" and go past it to the message. Clicking "yes" is liable to make the page hang. It's one of those things that means that an address on the page isn't properly formatted as far as the HTML portion is concerned. It probably has to do with the form in which the email is transmitted, if she is using a web version of email. As long as you can read the message, don't worry about it. Have you tried it in a different browser?