When trying to activate you get 0xC004F074 with description "The Key Management Server (KMS) is unavailable"

Error:

The kms host that is used is very probably a windows server 2008 KMS host that cannot standard activate windows 7 and 2008 r2 machines.

When you do not have Windows server 2008 r2 KMS host key have then you must have a Volume License agreement so that your request your Windows 7 and windows 2008 r2 kms keys.

Resolution

Step 1:
-If the KMS host a Windows server 2003 SP2 machine is you have the update from the KB article KB968915 install and restart the machine.
-If the KMS host a Windows server 2008 SP2 machine is you have the update from the KB article KB968912 install and start the new machine.
-If the KMS host one Windows Server 2008 R2 machine is you have to install any further update.

Step 2:
You the new KMS host key import now. The commands are as follows:

1. Uninstall KMS license Key on host – slmgr.vbs /upk

3. Activate KMS server online: slmgr.vbs /ato

4. Net Stop slsvc

5. Net Start slsvc

The clients can now activate