When I try to activate my Windows Server 2008 installation I receive an Error Code 0xC004C020, the error 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.

MAK – Multiple Activation Key
KMS – Key Management Service

Solution

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.

Over the phone activation

• 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 assign 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.