Volume activation error 0xC004C020

When I try to activate my Windows Server 2008 installation I receive the following: Error Code 0xC004C020, this prevents me from using the online activation to validate the installation.

0xC004C020 The activation server reported that the Multiple Activation Key has exceeded its limit.

When a Multiple Activation Key is used during an installation it checks with Microsoft and reduces the license pool by one, the size of the license pool is determined by the type of agreement. The user cannot reset the pool, this is why you have to call Microsoft once the limit has been reached.

MAKMultiple Activation Key
KMSKey Management Service


For this tutorial to work first attempt to validate the installation online.

  • Go to Start > Control Panel > System
  • At the bottom of the window search for and click on Change product Key
  • Enter the license key

If you receive an error like the one below preventing you from validating the installation then it will be necessary to call the Microsoft automated activation line.


  • Go to Start
  • Click on Run
  • And type SLUI 05

From the drop down list select the name of the country you live in. This is important because depending on the country you select you will be assigned a number to call.

  • Click the nearest location > United States
  • Click on Next

This window contains all the information you will need. Step 1 contains the number you need to call. Step 2 contains a series of unique numbers, you will need to provide the series of numbers to the operator (do not make mistakes). Step 3 If everything is Ok the operator will provide you with a confirmation ID, you will need to enter the numbers in the boxes located in Step 3 and press Enter.

The activation over the phone process is a simple one, try to use common sense when answering.

If the correct confirmation ID was provided you should be greeted with a new window confirming a genuine installation.

18 thoughts on “Volume activation error 0xC004C020”

  1. I tried the “over the phone” activation method, listed here as SLUI 04, and it doesn’t work. Just brings up the Windows Activation Error screen again. Tried SLUI 05 and that brought up the telephone option.

  2. Thanksssssssssssssssssssss Soooooooo muchhhhhhh now i validate my windows over phone, because my windows is from Dreamspark :D:D:D:D soooooo thankssss

  3. Huge Thanks from Bulgaria man !!! My Windows Server also working now ….. deam bastards 😉 from Dreamspark !!!!

  4. Just great, works for DreamSpark!

    It was really a PITA when i installed my new machine – god thanks i found this thread to understand activation with DreamsSpreak license of Server 2008 R2 🙂

  5. Brilliant . SLUI 05 Worked perfectly for Telephone Activation
    Thanks for that. Been battling this one for ages

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