Excel add-ins fail to load

Introduction

Update (Jan 10, 2021)

It seems the issue with add-ins including xl4 macro code being loaded with macros disabled has been fixed.

Update (Dec 14, 2020):

As of late Excel ignores add-ins which contain both VBA and the antiquated Excel 4 macro code. I have a couple of add-ins which have this combination because in some obscure cases it is the only way to access the formula property of an object.

What happens is that when you open the add-in directly using Windows Explorer or File, Open from Excel, the add-in loads but Excel does not prompt to enable macro's but silently disables them. Microsoft has confirmed this is a bug and has stated it will be fixed within the next weeks or so. In the mean time, you can manually install my add-ins by going through the add-ins dialog (the one immediately below) and clicking the Browse button.

End of update.

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.

The problem

Even though an add-in has been "installed" into Excel using the Add-ins dialog its userinterface does not show. This is that dialog (you get there by going to File, Options, Add-ins tab and pressing the Go... button):

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.

The cause

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.

Solution

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:

Other resources

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/