Excel Add-In: Can't Be Enabled

For sound security reasons, IT departments may restrict the use of Office add-ins to a pre-approved list. This can be done through a Microsoft Windows feature known as Group Policy. If you have installed the FastClose Excel Add-In, but it doesn't appear in the ribbon in Excel, and when you try to enable it, you can't, this could be the reason.

In Excel, navigate to File, Options, Add-Ins. Select 'COM Add-Ins' from the Manage drop down list and click Go.

If the FastClose add-in is listed but unticked, and at the bottom of the dialog it says "The add-in you have selected is disabled by your system administrator." then you need to get in touch with your IT department. Ask them to please amend group policy to allow the Excel add-in whose 'ProgId' is 'FastClose'.

More information can be found here: No Add-ins loaded due to group policy settings - Office 365

After they have done that, you will likely need to log out and back in, or restart, for the updated group policy to take effect on your PC.