Firewalls - If you are using a personal firewall (eg, ZoneAlarm) product on your computer, then it may be set to block all cookies. Consult the help pages on your firewall product if you need help allowing cookies through your firewall.
Clear your browser cache - If you are sure that you have enabled cookies and you are still getting an error page, then your browser may be showing an old (cached) copy of the error page. Try going to your browser options and using the delete/empty/clear temporary/cached pages from your computer, and then using the 'Reload' button on your browser to fetch a fresh copy of the Login as Existing User page.
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