Why won't my Windows 7 KMS key work on my Server 2008 KMS server?

Our Microsoft volume licensing site was recently updated to include our Windows 7 and Server 2008 R2 KMS keys. We have an existing KMS server running on Server 2008 (not R2). In an attempt to be proactive about supporting the new OSes in our environment, I unregistered the old KMS key with slmgr.vbs and tried registering the new key. The registration failed with Error 0xC004F050. The description for that error was "The Software Licensing Service reported that the product key is invalid."

What's wrong? I've checked and double checked that for typos against what is listed on the Volume Licensing website.

As it turns out, the version of the KMS software included with Server 2008 is version 1.1. In order to use Windows 7 and Server 2008 R2 KMS keys, you need to be running KMS 1.2. KMS 1.2 is included as part of Windows 7 and Server 2008 R2, but requires a separate download to run on Server 2008 (non-R2) or Server 2003.

I found the answer and more info on Microsoft's site: FAQ About Volume License Keys

KB article 968915 is now available and contains links to download KMS 1.2 for Windows 2003 Server. Here are direct links for x86 and x64.

KB article 968912 is now available and contains links to download KMS 1.2 for Windows Vista and Server 2008. Here are some direct links for Server 2008 (x86, x64, ia64) and Vista (x86 and x64).