Just came across an issue where autodiscover for Microsoft Exchange was not working when setting up Outlook 2010 SP2 on Windows XP.
The new customer was getting an SSL error message:
'Information you exchange with this site cannot be viewed or changed by others. However there is a problem with the site's security certificate.
The security certificate was issued by a company you have not chosen to trust. View the certificate to determine whether you want to trust the certifying authority.'
It turns out they had not installed Windows updates recently and had missed KB931125. After installing it worked right away.