Registry entry is Disabled..!!

This error occurs if the DisableRegistryTools Policy is enabled. With this policy enabled, you receive the following error message when you start the Registry Editor (regedit.exe):

For standalone Windows XP systems, perform the steps below to remove the registry editing restrictions.
Method 1: Using the REG.EXE console tool
1. Click Start, Run and type this command:

REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableRegistryTools /t REG_DWORD /d 0 /f

You should be able to launch Tweak UI, as well as the Registry Editor.

Method 2: Using the Group Policy Editor (Windows XP Professional only)
->Click Start, Run and type gpedit.msc and press ENTER
-> Go to the following location:

User Configuration Administrative Templates System
-> Double-click Disable registry editing tools and set it to Not Configured
-> Exit the Group Policy Editor

Note: If the setting already reads Not Configured, set it to Enabled, and click Apply. Then revert it back to Not Configured. This ensures that the DisableRegistryTools registry value is removed successfully.