When users attempt to use new keys available on Volume License Service Center in Key Management Service (KMS) in Windows 7 and or Windows Server 2008 R2, get a 0xC004f050 or 0xC004F015 errors. “With each release of Windows, Microsoft issue new product keys. In order for this key to be recognized on an earlier Windows release, its necessary to update license files used by software license service. Note that most common issue that customers ’re having while resolving above is, they don’t restart system before attempting to install new KMS host key. Without restart, new key’ll not be recognized and you’ll get same error.”
Reffer: KMS hosted on Windows Server 2003: In order to add support for Windows 7 and Windows Server 2008 R2, you’ll need to install the update found in KB 968195.
KMS hosted on Windows Server 2008 (and Windows Vista): KB 968912 has update and clearly defined steps to follow to update KMS host.