This issue happened in our production environment. The KMS activation failed on a WIndows 7 client due to a corrupt Token.dat file.
The solution was to stop the server, rename the token.dat file and restart the service again. Then activate the client against the KMS host.
- net stop sppsvc
- CD %windir%\ServiceProfiles\NetworkService\AppData\Roaming\Microsoft\SoftwareProtectionPlatform
- REN tokens.dat tokens.bar
- net start sppsvc
- slmgr /ipk 33PXH-7Y6KF-2VJC9-XBBR8-HVTHH (This client key should still be on the client)
- slmgr /ato