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
http://technet.microsoft.com/library/ee624357(office.14).aspx#section2

Download: Microsoft Office 2010 KMS Host License Pack
http://www.microsoft.com/en-us/download/details.aspx?id=25095

Deploy volume activation of Office 2013 / Prepare and configure the Office KMS host
http://technet.microsoft.com/en-us/library/ee624357(v=office.15).aspx#section2

Download: Microsoft Office 2013 Volume License Pack
http://www.microsoft.com/en-us/download/details.aspx?id=35584