Windows XP Service Pack 3 (SP3) installation: "Access Denied" error

If you are getting "Access Denied" error during installation of Service Pack 3 (standalone update for Windows XP) it’s probably caused by some kind of permission conflict. To fix this problem, try to close all applications (processes) running on your computer that could potentially protect the system. Applications, such as antivirus, spyware protection tools or any other kind of processes that are keeping the system safe, can limit access to parts of windows registry needed for service pack installation. After closing these applications, try to install windows service pack 3 update.

If the problem persists and your installation is again interrupted by "Access Denied" error, try this:

1. Download and install SubInACL.exe http://www.microsoft.com/downloads/details.aspx?FamilyID=e8ba3e56-d8fe-4a91-93cf-ed6985e3927b&displaylang=e

2. Copy the text below, paste it in notepad and save it as reset.cmd or you can also download it here.

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%\inf\defltbase.inf /db defltbase.sdb /verbose

3. Run reset.cmd you’ve created (this process can take some time).

4. Now you can install service pack 3.

This guide worked for me and I hope it will do the same for you.

Source: http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2873777&SiteID=17

source: http://filex.exofire.net