Q. I am unable to activate machines against my KMS server. How can I check why?
A. On the KMS server there are a number of actions to perform. Run the following command:
cscript slmgr.vbs /dlv
This will show the current count of machines using the KMS server, total requests, failed requests and a number of other items. The next step is to examine the Applications and Services Logs - Key Management Service log. In this log will be entries for each activation request. In the request will be a return code, the machine name and various other items. Within the log search for the machine name you are having problems with. A successful activation should have a 0x0 return code. Other values point to a problem, for example:
In this case the error code is C004F06C. Search for this error which will tell you the reason for the problem. In this case it is a time discrepancy more than 4 hours. A complete list of error codes can be found at https://technet.microsoft.com/en-us/library/dn502528.aspx.