Adding NumXL as Excel Trusted Publisher

Answer:

Adding the NumXL Add-in as an Excel Trusted Publisher can be done by following the steps below:

1. Click on the security warning message itself (not the “Enable Content” button).
   
2. Excel pops up the File “Info” screen.
   
3. Now, click on “Enable Content” (with the Shield icon) to open the menu, then click on “Advanced Options.” 
   
4. The Microsoft Security option now pops up and reports one or two issues related to NumXL and NumXLUI (Toolbar Add-in). Publishers of other add-ins might also be on this list.
   
5. Excel does not know the publisher, although the NumXL Add-in is digitally signed. To work around this issue, click “Trust all documents from this publisher” and/or "Enable all code published by this publisher.”
   
6. Repeat the exact resolution for the remaining issues of publishers that you trust (if any), and click OK when you're finished.
7. Restart Microsoft Excel so the changes take effect.