Outlook-+one+or+More+ActiveX+controls+could+not+be+displayed...

Problem:
When opening emails this message appears:

"One or More ActiveX controls could not be displayed because either:

1) Your current security settings prohibit running ActiveX controls on this page, or 2) You have blocked a publisher of one of the controls.

As a result, the page may not display correctly."

Solution:
Outlook was opening in safe mode. Re-opening Outlook in normal mode fixes the issue.