I have updated Office online many times. However, suddenly I got the message "Validation Incomplete: Office must be activated. ... I went to each Program in Office and checked (Help - Activate Product). Each time, the message was "This product is already activated". The same message appeared when I went through the steps suggested by Microsoft. Meanwhile, I am blocked from receiving the Updates for Office. What can I do, apart from re-installing Office with all its horrors?

That sounds rough... Where are you trying to update Office from? update.microsoft.com?