If you are attempting to set up an Office 2010 or Office 2013 KMS host by using the slmgr.vbs script, the "/ipk" switch, and a valid Office KMS host product key, the following error will occur:

Error: 0xC004F050 The software licensing service reported that the product key is invalid

Unlike Windows KMS host setup, Office KMS host setup involves installing a separate “KMS host license pack”, entering a related product key, and activating online or via phone.
See the following articles for additional information, to download the KMS host license packs, and step-by-step instructions for setting up Office KMS hosts:

Deploy volume activation of Office 2010 / Prepare and configure the KMS host

Download: Microsoft Office 2010 KMS Host License Pack

Deploy volume activation of Office 2013 / Prepare and configure the Office KMS host

Download: Microsoft Office 2013 Volume License Pack