Hi RRider, welcome to BC.
Only two things come to mind that normally would set off that security warning.
In Outlook, go to Tools>Options>Mail Format Tab.
Under the message format options, deselect the two "Use Microsoft Word" options.
If it still doesn't help, go to Tools>Options>Other Tab. Click the Advanced Options button, then the COM Add-ins button. An application in there may set it off as well. Remove one at a time. If you see Adobe's Acrobat listed, leave that one there. There is a reg fix that works better then just removing it.