Automation add-ins for Excel are not loading after installing April 2021 security update

Last Updated: April 28, 2021

ISSUE

After installing the April 2021 security update to Microsoft Office, some automation add-ins for Excel may not load and you could see a “Cannot run the macro” error message.

STATUS: WORKAROUND

To work around this issue, you will need to make a change in the registry. 

1. Identify the name of the automation add-in that fails to load. In later steps, we will refer to this name as <ProgID>.  To verify the add-in name, view your list of add-ins in the Excel Add-in Manager.

   1. From an open Excel sheet, select File, choose Options, and then choose the Add-Ins category.

   2. In the Manage box, select Excel Add-ins, and then choose Go. This will display the add-ins manager with your list of available add-ins.

2. From the Start menu, type regedit.exe in the search box, and then press Enter.
   If you are prompted for an administrator password or for confirmation, type the password or provide confirmation.

3. In Registry Editor, navigate to: HKEY_CLASSES_ROOT\<ProgID>

4. If a sub-key CurVer exists, retrieve the (default) value from the sub-key CurVer. Treat this as your new <ProgID> and repeat step 3. If a sub-key CurVer does not exist, continue to step 5.

5. Retrieve the (default) value from the sub-key CLSID - we will refer to this as <CLSID> in later steps.

6. Navigate in the registry to: HKEY_CLASSES_ROOT\<CLSID>\InprocServer32

7. If the (default) value is mscoree.dll, change it to C:\Windows\System32\mscoree.dll

8. Close Registry Editor

9. Close all Excel instances and then reopen Excel. Try the add-in again.