Good Afternoon Peter,
Thank you for your inquiry. Can you confirm the add-in is checked on in PowerPoint (go to File > Options > Add-ins > select the drop-down menu for 'Manage' > select COM Add-ins > Go > check 'on' ArcGIS Maps for Office) You may reference our online documentation here also.
Please let me know if this remedied the issue.
All the Best,
Shannon | Product Engineer | Maps for Office