If you are using Windows which is fully activated and a Genuine copy but one morning what if you find a Message as

Windows is not genuine
Your computer might not be running a counterfeit copy of Windows.

or System properties displays

You must activate today. Activate Windows now.

What would you do now; this is what one of my friend using Windows 7 faced one morning. If you have ever faced the similar situation and still looking for a solution then may be the following registry fix may solve the problem.

Actually this problem occurs when there is a lack of permissions on a registry key “HKEY_USERS\S-1-5-20”. Generally System, Network Service and Administrator accounts both have “Full Control” and “Read” permissions on this registry key but for any reason  “Network Service” doesn’t have proper permissions on this registry key thus causing the problem.

Solution:

1. First open Registry Editor by Typing regedit in RUN or Startmenu search box and press Enter.

2. Now locate the following key:

HKEY_USERS\S-1-5-20

3. Right-click on “S-1-5-20” key and select “Permissions…”. It’ll open a new window as shown below:

4. Select “NETWORK SERVICE” in user list and check “Allow” box given for “Full Control” permission. Click on OK button to apply the changes.

NOTE: If “NETWORK SERVICE” is not present in user list, click on “Add” button. Now type Network Service in “Enter the object names to select type” and click on “Check Names” button. It’ll detect and confirm the username. Click on OK button.

5. That’s it. Restart your system and your problem should be fixed.