Office 2013 fails to activate from KMS host when Office 2013 is installed on windows 8.1 and the KMS is hosted on server 2008 r2

Any attempt to activate Office 2013 installed on a windows 8.1 computer fails with a "licence key is invalid" message when the KMS is installed on a server running windows 2008 R2. I've installed KB2885698 and VAMT 3.1 but this has made no difference. Office 2013 installed on earlier windows versions activates fine.

Help!