Help me bypassing "Access Denied" errors on Windows Registry during XP's setup

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By the way, I forgot to post the code of the CMD file I'm using, so here it is:

Code:

REG ADD "HKLM\SYSTEM\WPA\MediaCenter" /v Installed /t REG_SZ /d 1 /f
start /wait rundll32 setupapi.dll,InstallHinfSection Freestyle 128 medctroc.inf
EXIT

And this is the code for SVCPACK.INI:

Code:

[CatalogHeader]

[Version]
BuildNumber=2600
MinorVersion=1
MajorVersion=5
Signature="$WINDOWS NT$"
[SetupData]
CatalogSubDir="\I386\svcpack"
[SetupHotfixesToRun]
MEDIACTR.CMD
[ProductCatalogsToInstall]

 

Thank you for replying! My project goal is to not use any 3rd-party tool (so only what Windows can do built-in, such as CMD) in order to be as clean as possible, as I did with Windows XP 2005 Edition.
There's no known workaround for this Access Denied issue?