Outlook must be in 32 bit: http://social.microsoft.com/Forums/en-US/partnerdynamicsnav/thread/2aab2361-be61-4897-a9cd-76c5b9726f32
If you do not have access to that site, then refer to http://blogs.msdn.com/b/nav/archive/2010/08/20/microsoft-dynamics-nav-compatibility-with-microsoft-office-2010-and-microsoft-sharepoint-2010.aspx