Excel add-ins fail to load
Lately (I wrote this page on August 17, 2016) I've been getting reports from people complaining that they can no longer use add-ins. In this article I describe the problem and a solution.
Even though an add-in has been "installed" into Excel using the Add-ins dialog its userinterface does not show. This is that dialog:
As you can see, some add-ins are checked. But sometimes the user-interface of an add-in fails to display. In fact, the add-in file will not open in Excel at all, even if you try from Windows Explorer, or from File, Open from within Excel. Without any error message.
A recent Office Security update has caused any file downloaded from the internet (so this includes add-ins) to be marked as Blocked. Even if those files were in a zip container, they are marked as blocked. And Excel will simply not open them.
Unblock the files! Like so:
1. Copy the file from the zip file to any folder
2. Right-click the file and choose properties:
3. Click the Unblock button:
If you have a folder full of blocked files, this page describes a way to unblock all of them using Powershell.
And a great article by fellow-MVP Jon Acampora: Excel Add-in Ribbon Disappears After Installation.
This article describes the mechanics of the problem very well: http://www.howtogeek.com/70012/what-causes-the-file-downloaded-from-the-internet-warning-and-how-can-i-easily-remove-it/