Why am I unable to Merge Content from an active presentation in Classic Authoring?

If you cannot merge content from an active presentation, and you are the Author or a Company Administrator for the presentation, check to be sure that the presentation is set to allow copying. 

To check this setting follow the steps below:

• Edit Presentation
• Navigate to the Security tab
• Select Allow authors to copy this presentation

Presentations must be set to allow copying if they are to be merged.