This is an issue experienced by all applications and is due to the tight security of Windows and Outlook. See this Microsoft article for details:
http://office.microsoft.com/en-us/outlook/HA012299431033.aspx
Your two options are (1) to ensure that your antivirus program is running and has the latest updates, or (2) use a third-party tool (such as ClickYes) to handle the manual interaction successfully.