This is the information I have received from Sage:

The problem has been caused by a Microsoft Office Security update.

 There is no imminent fix for this but we are keeping a list of all Sage 200 customers who have had the problem for future communications.

The name of the business partner, your customer, and yourself have been added as contacts.

We are closing the cases on the Case Management database and storing the contacts for future communications.

We recommend uninstalling the updates or reverting back to the version of Office you were using prior to the problem

For Office 2016 and below, if you can see the Update in “Installed Updates” on the machine, un-install the update.

e.g. Go to Control Panel> Programs> Programs and Features> Installed Updates>  ( or the equivalent Installed Updates for the operating system of your pc )

The updates that went out are listed here -

https://support.microsoft.com/en-us/topic/april-2021-updates-for-microsoft-office-8621a088-37ba-403a-a3b7-73617a7017ee

Some clients have had to uninstall the whole Office software, but others got it working on Office 2013 by uninstalling just Security Update for Office 2013 (KB4504726).

The equivalent one for Office 2016 (KB4504722) may work on that version if you install just the Security Update.

For users on Microsoft Office 365 full version, they would have to revert to an earlier version of Office.

Then turn off Automatic Updates. NOTE: Office 365 is not officially tested or supported with Sage 200 Business Intelligence

For Office 365, and anyone who doesn't have the updates listed in Control Panel, they could try this to revert back to an earlier version

https://support.microsoft.com/en-us/topic/how-to-revert-to-an-earlier-version-of-office-2bd5c457-a917-d57e-35a1-f709e3dda841