Slui.exe 0x2a 0x8007267C KMS Activation Troubleshooting Steps Table 2 describes common issues that can occur during KMS activations as well as steps for resolving them. Running Microsoft Windows non-core edition, run 'slui.exe 0x2a. So if I were to have a Windows Server 2008 R2 KMS key, I could have activated that server with the appropriate Windows Server 2008 R2 KMS key, then use it to activate Windows 7 clients.
As confusing as that sounds, what it really means is that any operating system with a newer operating system can usually activate lower operating systems.
