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.

  • Eric

    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.

    • dataninja

      Try the steps again but this time disconnect the system from the Internet.

  • Guilherme Navarro

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

  • boga

    thanks eric… 05 does the trick!

  • Teodor

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

  • Paul

    Thanks, worked great. Thank you and thanks DreamSpark.

  • man this is the shit I really appreciated it works guys just follow the instructions.

  • Pave;

    Thank you. Thank you Microsoft and thank you Dream Spark!

  • Just Great

    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 🙂

  • djaka boyn

    thanks, this works well for me, live from The Netherlands,,


  • bruce

    Thanks a lot! Its function on win7 pro (64) also. thx from germany!

  • Mick

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

  • Corvon

    Just wanted to say thanks for the info, now I can continue to learn Windows Server 2008 R2!

  • Hasan

    it works 100%. no problem

  • Hasan

    it works 100%. no problem. thanks a lot

  • bhaskar

    wow !! thnx a lot buddy..it helped 🙂

  • Nach0

    Dude YES!! I thought I was S.O.L Worked on Windows 7 Enterprise.
    Many thanks!!

  • Dave Chronister

    For windows 8 the command uses 04 instead of 05