I am using Outlook 2003. I had been receiving frequent requests for my password. This has now stopped. All emails staarted coming in twice. Following the advice at
http://www.howto-outlook.com/faq/duplicates.htm I have switched off checking incoming (and outgoing) mail for viruses. This has stopped emails received when Outlook is open being being displayed twice. But when Outlook is opened the whole list of mail in the pipeline still comes in twice.