Recreate Windows Licensing Store
(W7) If you have a valid copy of Window’s but you get this error, follow these steps to recreate the Licensing Store within Windows.
Search => Command Prompt (As Administrator) =>
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net stop sppsvc cd C:\WINDOWS\ServiceProfiles\NetworkService\AppData\Roaming\Microsoft\SoftwareProtectionPlatform rename tokens.dat tokens.bar cd %windir%\system32 net start sppsvc slui.exe
After a couple of seconds Windows Activation dialog will appear. You may be asked to re-activate and/or re-enter your product key or Activation may occur automatically.
If unsuccessful, try going here.