Fix for “Access Denied” Error when installing windows XP SP3

These errors can occur if permissions for one or more registry keys are restricted in a way that prevents the service pack from updating the keys. Registry keys can become restricted by certain programs that change the system access control lists (SACL) in the Registry so that administrator accounts cannot alter them. The service pack installer runs under an administrator account (User), and therefore cannot access restricted registry keys. If Windows XP Service Pack cannot update a registry key because it is restricted by another program, the service pack installation fails.



Procedure to follow
1) Download and then install the Subinacl.exe file from here
2) Start Notepad
Copy and then paste the following text into Notepad.
cd /d "%ProgramFiles%\Windows Resource Kits\Tools"
subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=administrators=f /grant=system=f
subinacl /subkeyreg HKEY_CURRENT_USER /grant=administrators=f /grant=system=f
subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=administrators=f /grant=system=f
subinacl /subdirectories %SystemDrive% /grant=administrators=f /grant=system=f
subinacl /subdirectories %windir%\*.* /grant=administrators=f /grant=system=f
secedit /configure /cfg %windir%\repair\secsetup.inf /db secsetup.sdb /verbose
3) Save this file as sp3fix.bat
Double-click the sp3fix.bat file to run the script.
Note This script file may take a long time to run. You must run this script as an administrator.
After completing the above script you can Install Windows XP SP3

.