Product:
Cognos Controller 10.3
Microsoft Windows 2012 R2 server

Problem:
One user does not get the Cognos Controller menu to work inside Microsoft Excel 365.
When user try to add the COM add in there is a error like COM import fail.

Solution:
Close Excel and Close Cognos Controller Client.
Enter REGEDIT on run command on start menu on users laptop.
Inside [HKEY_CURRENT_USER\Software\Microsoft\Office\Excel]
Right click on Excel branch and select export

Save the file as regbackup.reg in a location you can find (d:\temp)
The delete the rows below addins, that is for Cognos Controller.
[HKEY_CURRENT_USER\Software\Microsoft\Office\Excel\Addins]

Start Cognos Controller client on your laptop and login in.
Click on the icon for excel inside Cognos Controller client.
This should start the Excel program locally, and also install the Controller link to excel again. This take time, as the start of Excel is slow. When excel is fully started, check that the controller menu work.

More information
https://www.ibm.com/support/pages/controller-excel-link-microsoft-excel-addin-was-disabled-when-opening-data-entry-form
https://www.ibm.com/support/pages/troubleshooting-failed-register-excellink-addin-add-method-addins-class-failed-error-when-using-excel-link
https://www.ibm.com/support/pages/troubleshooting-controller-excel-link-com-add-disappears-each-time-excel-closed-relaunched