Error on WWI server &1: Another generation service is blocking Word

What causes this issue?

Another generation service has been blocking Microsoft Word for some
time, which means that Microsoft Word cannot be loaded for the current
generation service.

System Response

Generation was not carried out.

How to fix this error?

Check whether the services are set up correctly on the generation
server.
Check the Windows event log on the WWI generation server. The event log
may contain other error messages.

Error message extract from SAP system. Copyright SAP SE.